Ion-sensitive electrode and processes for making the same

• US 4,133,735 A
• Filed: 09/27/1977
• Issued: 01/09/1979
• Est. Priority Date: 09/27/1977
• Status: Expired due to Term

• Current Assignee: Board of Regents of The University of Washington (University of Washington)
• Original Assignee: Board of Regents of The University of Washington (University of Washington)
• Inventors: Afromowitz, Martin A., Yee, Sinclair S.
• Primary Examiner(s): Kaplan, G. L.
• Application Number:
  US05/837,279
• Time in Patent Office: 469 Days
• Field of Search: 204/195 M, 204/195 G, 204/192 SP, 128/2 E, 128/2.1 E, 29/592 R, 324/29, 324/30 R, 427/123, 427/124, 427/125
• US Class Current: 204/406
• CPC Class Codes: G01N 27/3335 the membrane containing at least one organic component G01N27/3271 takes precedence; aspects concerning the enzyme reagent in enzyme electrodes C12Q1/001
• CPC Class Codes: G01N 27/36 Glass electrodes
• CPC Class Codes: H01L 2224/05599 Material
• CPC Class Codes: H01L 2224/45015 being circular
• CPC Class Codes: H01L 2224/45099 Material
• CPC Class Codes: H01L 2224/45139 Silver (Ag) as principal constituent
• CPC Class Codes: H01L 2224/45144 Gold (Au) as principal constituent
• CPC Class Codes: H01L 2224/45147 Copper (Cu) as principal constituent
• CPC Class Codes: H01L 2224/48091 Arched
• CPC Class Codes: H01L 2224/48137 the bodies being arranged next to each other, e.g. on a common substrate
• CPC Class Codes: H01L 2224/48227 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/4903 Connectors having different sizes, e.g. different diameters
• CPC Class Codes: H01L 2224/49505 Connectors having different materials
• CPC Class Codes: H01L 2224/85205 Ultrasonic bonding
• CPC Class Codes: H01L 24/45 of an individual wire connector
• CPC Class Codes: H01L 24/48 of an individual wire connector
• CPC Class Codes: H01L 24/49 of a plurality of wire connectors
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00011 Not relevant to the scope of the group, the symbol of which is combined with the symbol of this group
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/01047 : Silver [Ag]
• CPC Class Codes: H01L 2924/01049 : Indium [In]
• CPC Class Codes: H01L 2924/01322 : Eutectic Alloys, i.e. obtained by a liquid transforming into two solid phases
• CPC Class Codes: H01L 2924/10253 : Silicon [Si]
• CPC Class Codes: H01L 2924/1306 : Field-effect transistor [FET]
• CPC Class Codes: H01L 2924/14 : Integrated circuits
• CPC Class Codes: H01L 2924/15787 : Ceramics, e.g. crystalline carbides, nitrides or oxides
• CPC Class Codes: H01L 2924/207 : Diameter ranges
• CPC Class Codes: H01L 2924/3011 : Impedance
• CPC Class Codes: H01L 2924/3025 : Electromagnetic shielding
• CPC Class Codes: Y10T 29/49002 : Electrical device making

Abstract

An improved ion-sensitive electrode is described, particularly in terms of the structure of a pH electrode and first and second processes for making the same. The pH electrode includes a substrate, preferably of forsterite, which is configured as a wafer having a substantially planar wafer surface. A continuous conducting layer, formed by either thin-film vapor deposition or thick-film screening processes, is formed on the substantially planar wafer surface in a desired configuration. A first region of the continuous conducting layer, and contiguous portions of the substantially planar wafer surface, are covered by a continuous membrane layer preferably composed of a pH-sensitive glass such as Corning Code 0150 glass. Typically, the membrane layer is formed by a thick-film process which involves the reduction of the glass to a fine powder, the mixing of the powder with an organic vehicle including an organic solvent and an organic binder to form a glass paste, and the application of the glass paste to the wafer through a wire mesh screen having an open region therethrough corresponding in configuration to that of the desired membrane layer. The paste when applied to the wafer is fused into a continuous membrane layer by the application of heat, at a first temperature to drive off the organic solvent and at a second temperature or temperatures to drive off the organic binder and to fuse the glass. An insulated output lead is connected directly to a second region of the conducting layer. Alternatively, an active device chip, such as that including a field effect transistor, is bonded to the wafer and interconnected with the second region of the conducting layer and with the output lead or leads. The exposed conducting elements of the electrode, including the second region of the conducting layer, the active device chip, and all exposed portions of the leads, are covered by a fluid-tight seal. Other ion-sensitive electrodes and variations of the aforementioned processes are described.

Claims

1. An improved ion-sensitive electrode comprising:

(a) a substrate formed into a wafer having a substantially planar wafer surface;

(b) a conductor bonded to said wafer, said conductor having first and second regions, with at least said first region being formed as a conducting layer on said substantially planar wafer surface;

(c) an ion-sensitive membrane bonded to said wafer and to at least a portion of said conductor, said membrane including a continuous membrane layer covering said first region of said conductor and portions of said substantially planar wafer surface contiguous to said first region of said conductor;

(d) output means connected to said second region of said conductor for interconnecting said electrode with a utilization device; and

(e) fluid-tight sealing means bonded to said wafer, to said conductor, and to said output means, said fluid-tight sealing means covering at least said second region of said conductor and portions of said wafer and said output means adjacent said second region of said conductor.

2. An electrode as recited in claim 1, wherein said ion-sensitive membrane is formed from a glass paste including an ion-sensitive glass substantially by a thick-film screening process, and wherein said substrate is a ceramic material having a coefficient of thermal expansion which is compatible with that of said ion-sensitive glass.

3. An electrode as recited in claim 2, wherein said ion-sensitive glass is a pH-sensitive glass.

4. An electrode as recited in claim 3, wherein said conductor includes a plurality of metallic layers which are formed in succession on said wafer by a vapor-deposition process.

5. An electrode as recited in claim 3, wherein said conducting layer is formed from a paste including at least one conducting material by a thick-film screening process.

6. An electrode as recited in claim 3, wherein said pH-sensitive glass is Corning Code 0150 glass, and wherein said substrate is forsterite.

7. An electrode as recited in claim 6, wherein said conductor includes a plurality of metallic layers which are formed in succession on said wafer by a vapor-deposition process.

8. An electrode as recited in claim 7, wherein said plurality of metallic layers are composed, in succession, of chromium, nickel, gold and silver.

9. An electrode as recited in claim 6, wherein said conducting layer is formed from a metal paste including a mixture of a plurality of metals by a thick-film screening process.

10. An electrode as recited in claim 9, wherein said plurality of metals include platinum and gold.

11. An electrode as recited in claim 1, wherein said conductor comprises a plurality of metallic layers formed in succession on said wafer by a vapor-deposition process.

12. An electrode as recited in claim 1, wherein said conducting layer is formed from a paste including at least one conducting material by a thick-film screening process.

13. An electrode as recited in claim 1, wherein said first and said second regions of said conductor are both formed as a continuous conducting layer on said substantially planar wafer surface.

14. An electrode as recited in claim 13, wherein said continuous conducting layer has a configuration of a first elongated strip having first and second ends which are enlarged with respect to said first elongated strip, with said first end and a portion of said elongated strip adjacent thereto comprising said first region of said conductor, and with said second end and the remaining portion of said elongated strip comprising said second region of said conductor.

15. An electrode as recited in claim 14, wherein said membrane layer has a configuration of a second elongated strip having an enlarged end, said enlarged end and said second elongated strip being complementary to but slightly larger than said first end and the portion of said first elongated strip of said conducting layer comprising said first region of said conductor.

16. An electrode as recited in claim 15, wherein said fluid-tight sealing means is also bonded to said membrane layer and covers in addition a portion of said membrane layer adjacent said second region of said conductor.

17. An electrode as recited in claim 14, wherein said continuous conducting layer further has the configuration of at least one conducting pad formed on said substantially planar wafer surface, said conducting pad being isolated from said elongated strip and adjacent said second end thereof;

and, wherein said output means includes an active device chip bonded to said substantially planar wafer surface adjacent said second end of said elongated strip and said conducting pad, said active device chip having an input terminal and at least one output terminal;

said output means further including first interconnecting lead means connected to said second end of said elongated strip and said input terminal of said active device chip, second interconnecting lead means connected to said output terminal of said active device chip and said conducting pad, and output lead means connected to said conducting pad for interconnecting said electrode with a utilization device; and

, wherein said fluid-tight sealing means is bonded to and covers said active device chip, said first and second interconnecting lead means, and a portion of said output lead means immediately adjacent said conducting pad.

18. An electrode as recited in claim 17, wherein said active device chip includes a field effect transistor.

19. An electrode as recited in claim 13, wherein said output means includes an active device chip bonded to said wafer, said active device chip having an input terminal and at least one output terminal;

interconnecting lead means connected to said second region of said conductor and said input terminal of said active device chip; and

, output lead means connected to said output terminal of said active device chip for interconnecting said electrode with a utilization device; and

, wherein said fluid-tight sealing means is also bonded to and covers said active device chip, said interconnecting lead means, and a portion of said output lead means immediately adjacent said output terminal on said active device chip.

20. An electrode as recited in claim 19, wherein said active device chip includes a field effect transistor.

21. An electrode as recited in claim 19, wherein said active device chip is bonded to said substantially planar wafer surface adjacent said second region of said conductor.

22. An electrode as recited in claim 13, wherein said output means includes an output lead connected to said second region of said conductor for interconnecting said electrode with a utilization device;

and, wherein said fluid-tight sealing means is bonded to and covers a portion of said output lead immediately adjacent said second region of said conductor.

23. An electrode as recited in claim 1, wherein said output means includes an active device chip bonded to said wafer, said active device chip having an input terminal and at least one output terminal;

interconnecting lead means connected to said second region of said conductor and said input terminal of said active device chip; and

, output lead means connected to said output terminal of said active device chip for interconnecting said electrode with a utilization device; and

, wherein said fluid-tight sealing means is also bonded to and covers said active device chip, said interconnecting means, and a portion of said output lead means immediately adjacent said output terminal of said active device chip.

24. An electrode as recited in claim 23, wherein said active device chip includes a field effect transistor.

25. An electrode as recited in claim 23, wherein said active device chip is bonded to said substantially planar wafer surface adjacent said second region of said conductor.

26. An electrode as recited in claim 1, wherein said output means includes an output lead connected to said second region of said conductor for interconnecting said electrode with a utilization device;

and, wherein said fluid-tight sealing means is bonded to and covers a portion of said output lead immediately adjacent said second region of said conductor.

27. An electrode as recited in claim 1, wherein said fluid-tight sealing means comprises:

a body having a cavity therein, said wafer being received in said cavity so that said body covers at least said second region of said conductor and portions of said wafer adjacent said second region; and

, a potting material contained within and filling said cavity.

28. An electrode as recited in claim 27, wherein said body comprises a length of glass tubing, and said potting material comprises an epoxy resin.

29. An electrode as recited in claim 27, wherein said body comprises a length of heat-shrinkable tubing, and said potting material comprises beeswax.

30. An electrode as recited in claim 1, wherein said ion-sensitive membrane is formed from a polymer loaded with an ion-exchanging material.

31. An electrode as recited in claim 30, wherein said polymer is polyvinyl chloride.

32. An electrode as recited in claim 30, wherein said ion-exchanging material is calcium didecylphosphate.

33. An electrode as recited in claim 30, wherein said ion-exchanging material is valinomycin.

34. An electrode as recited in claim 30, wherein said electrode further comprises a layer of inner reference material interposed between said first region of said conductor and said ion-sensitive membrane.

35. A process for fabricating an ion-sensitive electrode, said process comprising the steps of:

(a) fabricating a wafer from a substrate material, said wafer having a substantially planar wafer surface;

(b) forming a continuous conducting layer having a desired configuration on said substantially planar wafer surface;

(c) forming a continuous ion-sensitive membrane layer on a first region of said continuous conducting layer and portions of said substantially planar wafer surface contiguous to said first region of said continuous conducting layer;

(d) connecting at least one lead to a second region of said continuous conducting layer; and

(e) forming a fluid-tight seal over at least said second region of said continuous conducting layer, portions of said substantially planar wafer surface contiguous to said second region, and a portion of said lead adjacent said second region.

36. A process as recited in claim 35, wherein said continuous conducting layer is formed by a thin-film, vapor deposition subprocess.

37. A process as recited in claim 36, wherein said thin-film, vapor deposition subprocess includes the substeps of:

(a) polishing and cleaning said substantially planar wafer surface;

(b) placing said wafer into an evacuated chamber along with a quantity of at least one metal, and heating said metal to a temperature sufficient to vaporize said metal so that said metal uniformly deposits in a continuous conducting layer on at least said substantially planar wafer surface;

(c) removing said wafer from said evacuated chamber; and

(d) photoetching said continuous conducting layer to leave on said substantially planar wafer surface only that portion of said continuous conducting layer having the desired configuration.

38. A process as recited in claim 37, wherein said thin-film, vapor deposition subprocess includes the further substeps of placing a quantity of at least one other metal into said evacuated chamber and heating said one other metal in succession to said one metal to uniformly deposit said one other metal in a successive continuous layer upon said wafer.

39. A process as recited in claim 35, wherein said continuous conducting layer is formed by a thick-film screening subprocess.

40. A process as recited in claim 39, wherein said thick-film screening subprocess includes the substeps of:

(a) preparing a first wire mesh screen having a predetermined mesh and a thickness approximating that of the desired conducting layer, said first wire mesh screen also having an open region therethrough corresponding in configuration to that of the desired conducting layer;

(b) preparing a paste by mixing, with an organic vehicle including an organic solvent and an organic binder, a conducting material in particle form, said conducting material having an average particle size less than said predetermined mesh of said first wire mesh screen;

(c) bringing said first wire mesh screen into contact with said substantially planar wafer surface and spreading said paste on said wire mesh screen to cover at least said open region therethrough;

(d) forcing said paste through said open region in said first wire mesh screen and into contact with said substantially planar wafer surface; and

,

(e) removing said first wire mesh screen and heating said wafer to a first temperature for a time sufficient to drive off said organic solvent and then to at least a second temperature for a time sufficient to drive off said organic binder and to fuse said conducting material into a continuous conducting layer; and

,

(f) allowing said wafer to cool.

41. A process as recited in claim 40, wherein said conducting material includes at least one metal.

42. A process as recited in claim 35, wherein said ion-sensitive membrane layer is formed by a thick-film screening subprocess.

43. A process as recited in claim 42, wherein said thick-film screening subprocess includes the substeps of:

(a) preparing a second wire mesh screen having a predetermined mesh and a thickness approximating that of the desired ion-sensitive membrane layer, said second wire mesh screen having an open region therethrough corresponding in configuration to that of the desired ion-sensitive membrane layer;

(b) preparing a membrane paste by mixing, with an organic vehicle including an organic solvent and an organic binder, a paste material including an ion-sensitive membrane material in particle form, said ion-sensitive membrane material having an average particle size less than said predetermined mesh of said second wire mesh screen;

(c) bringing said second wire mesh screen into contact with said substantially planar wafer surface so that said open region therein is in registration with said continuous conducting layer, and spreading said membrane paste on said second wire mesh screen to cover at least said open region therethrough;

(d) forcing said membrane paste through said open region in said second wire mesh screen and into contact with said conducting layer and contiguous portions of said substantially planar wafer surface;

(e) removing said second wire mesh screen and heating said wafer to a first temperature for a time sufficient to drive off said organic solvent, and then to at least a second temperature for a time sufficient to drive off said organic binder and to fuse said membrane material into a continuous ion-sensitive layer; and

(f) quickly quenching said wafer to substantially room temperature.

44. A process as recited in claim 43, wherein said substeps (c), (d), (e) and (f) are repeated until a continuous, pin-hole free, ion-sensitive membrane layer is formed.

45. A process as recited in claim 43, wherein said ion-sensitive material is an ion-sensitive glass.

46. A process as recited in claim 45, wherein said second temperature is approximately the working point of said ion-sensitive glass.

47. A process as recited in claim 35, further comprising the steps of:

(a) bonding an active device chip to said substantially planar wafer surface, said active device chip including an input terminal and at least one output terminal;

(b) bonding a first lead to said second region of said conducting layer and to said input terminal of said active device chip;

(c) connecting a second lead to said output terminal of said active device chip; and

,

(d) forming said fluid-tight seal additionally over said first lead, said active device chip, and a portion of said second lead adjacent said active device chip.

48. A process as recited in claim 47, further comprising the steps of:

(a) forming said continuous conducting layer into a configuration also including a pad isolated from said second region thereof on said substantially planar wafer surface;

(b) bonding a third lead to said output terminal of said active device chip and to said pad;

(c) connecting said second lead to said pad; and

(d) forming said fluid-tight seal additionally over said third lead and said pad.

49. A process as recited in claim 35, wherein said step of forming said fluid-tight seal includes the substeps of:

(a) flattening one end of a length of tubing to define a cavity therein complementary in configuration to said wafer;

(b) passing said at least one lead through said length of tubing and out the other end thereof and inserting said wafer into said cavity so that said flattened end overlies at least all of said second region of said continuous conducting layer; and

(c) completely filling said cavity with a potting material.

50. A process as recited in claim 49, wherein said tubing is composed of glass.

51. A process as recited in claim 49, wherein said potting material is an epoxy resin.

52. A process as recited in claim 35, wherein said step of forming said fluid-tight seal includes the substeps of:

(a) filling one end of a length of heat-shrinkable tubing with a potting material and forming a cavity in said potting material which is complementary in configuration to said wafer;

(b) passing said at least one lead through said length of heat-shrinkable tubing and out the other end thereof, and inserting said wafer into said cavity so that said length of heat-shrinkable tubing overlies at least all of said second region of said continuous conducting layer; and

(c) heating said wafer so that said heat-shrinkable tubing conforms to said wafer.

53. A process as recited in claim 52, wherein said heat-shrinkable tubing is composed of polyvinyl chloride.

54. A process as recited in claim 52, wherein said potting material is composed of beeswax.

55. A process for fabricating a pH electrode, said process comprising the steps of:

(a) fabricating a wafer from a ceramic substrate material, said wafer having a substantially planar wafer surface;

(b) forming a continuous conducing layer having a desired configuration on said substantially planar wafer surface;

(c) forming a continuous membrane layer from a pH-sensitive glass on a first region of said continuous conducting layer and portions of said substantially planar wafer surface contiguous to said first region, said ceramic substrate material having a coefficient of thermal expansion compatible with that of said pH-sensitive glass;

(d) connecting at least one lead to a second region of said continuous conducting layer; and

(e) forming a fluid-tight seal over at least said second region of said continuous conducting layer, portions of said substantially planar wafer surface contiguous to said second region, and a portion of said lead adjacent said second region.

56. A process as recited in claim 55, wherein said pH-sensitive glass has a nominal mole-percent composition of 22% Na₂ O, 6% CaO, and 72% SiO₂, and said ceramic substrate material is forsterite.

57. A process as recited in claim 56, wherein said step of forming said continuous conducting layer is accomplished by forming in succession a plurality of thin-film layers of chromium, nickel, gold and silver in the configuration of the desired conducting layer, and wherein said lead is connected by soldering to said second region of said conducting layer.

58. A process as recited in claim 57, wherein said chromium, nickel, and gold layers have thicknesses of approximately 656 A, 268 A and 37 8 A, respectively and wherein said silver layers has a thickness in the range of 1400-2000 A.

59. A process as recited in claim 56, wherein said step of forming said continuous conducting layer is accomplished by thick-film screening of a metal paste.

60. A process as recited in claim 59, wherein said step of forming a continuous conducting layer comprises the substeps of:

(a) preparing a metal paste consisting of gold of approximately 60 weight-percent, platinum of approximately 11 weight-percent, both said gold and said platinum being in fine particle form, said metal paste also consisting of glass particles and other oxide particles, and also consisitng of an organic vehicle including an organic binder and an organic solvent;

(b) preparing a first wire mesh screen of at least 200 wire mesh and a thickness of approximately 2 mils, said first wire mesh screen having an open region therethrough corresponding in configuration to that of the desired conducting layer;

(c) bringing said first wire mesh screen into contact with said substantially planar wafer surface and spreading said metal paste on said wire mesh screen to cover at least said open region therethrough;

(d) forcing said metal paste through said open region in said first wire mesh screen and into contact with said substantially planar wafer surface;

(e) removing said first wire mesh screen and heating said wafer under an infrared lamp for approximately 15 minutes to drive off said organic solvent, then heating said wafer to a temperature of approximately 500°

C. for 45 minutes and then to a temperature of 950°

C. for approximately 10 minutes to drive off said organic binder and to fuse said gold and platinum into a continuous conducting layer; and

(f) allowing said wafer to cool.

61. A process as recited in claim 56, wherein said membrane layer is formed from a glass paste including said pH sensitive glass.

62. A process as recited in claim 61, wherein said step of forming said membrane layer comprises the substeps of:

(a) reducing said pH sensitive glass to a fine powder having an average particle size of approximately 1 micron;

(b) mixing said fine powder with an organic vehicle including an organic binder and an organic solvent to form a glass paste, said glass paste comprising approximately 60-75 weight-percent of said pH sensitive glass;

(c) applying said glass paste to said wafer so that said glass paste overlies said first region of said continuous conducting layer and contiguous portions of said substantially planar wafer surface;

(d) heating said wafer to a first temperature for a period of time sufficient to drive off said organic solvent;

(e) heating said wafer to at least a second, higher temperature for a period of time sufficient to drive off said organic binder and to fuse said glass into a continuous membrane layer; and

(f) quickly quenching said wafer to substantially room temperature.

63. A process as recited in claim 62, wherein said first temperature is approximately 100°

C. and wherein said wafer is maintained at said first temperature for approximately 10 minutes.

64. A process as recited in claim 62, wherein said second temperature is approximately 1000°

C., and wherein said wafer is maintained at said second temperature for approximately 8 minutes.

65. A process as recited in claim 62, wherein said substep (c) is accomplished by preparing a second wire mesh screen of at least 200 mesh and a thickness of approximately 2 mils, said second wire mesh screen having an open region therethrough corresponding in configuration to that of the desired membrane layer;

bringing said second wire mesh screen into contact with said substantially planar wafer surface so that said open region therethrough is in registration with said continuous conducting layer; and

spreading said glass paste onto said second wire mesh screen to cover at least said open region therethrough;

forcing said glass paste through said open region in said second wire mesh screen and into contact with said first region of said continuous conducting layer and contiguous portions of said substantially planar wafer surface; and

removing said second wire mesh screen.

66. A process as recited in claim 65, wherein said first temperature is that obtained when the wafer is placed under an infrared lamp, and wherein said wafer is maintained under said infrared lamp for approximately 5 minutes.

67. A process as recited in claim 65, wherein said substep (e) is achieved by placing the wafer in a furnace, the furnace having been previously heated to a temperature of approximately 500°

C., and maintaining the wafer in the furnace at approximately 500°

C. for approximately 1 hour, and thereafter raising the temperature of the furnace to approximately 850°

C. and removing the wafer from the furnace as soon as the temperature reaches approximately 850°

C.

68. A process for fabricating an ion-sensitive electrode, said process comprising the steps of:

(a) fabricating a wafer from a ceramic substrate material, said wafer having a substantially planar wafer surface;

(b) forming a continuous conducting layer having a desired configuration on said substantially planar wafer surface, said continuous conducting layer being divided into first and second regions;

(c) connecting at least one lead to said second region of said continuous conducting layers;

(d) forming a fluid-tight seal over said second region of said continuous conducting layer, portions of said substantially planar wafer surface contiguous to said second region, and a portion of said lead adjacent said second region; and

(e) forming an ion-sensitive membrane on said wafer by dipping said wafer into a solution including a polymer, an ion-exchanging material, and a solvent therefor so that said solution covers at least said first region of said continuous conducting layer, and removing said wafer from said solution and allowing said solvent to evaporate.

69. A process as recited in claim 68, wherein said membrane is sensitive to calcium ions and said ion-exchanging material is calcium didecylphosphate.

70. A process as recited in claim 69, wherein said polymer is polyvinyl chloride.

71. A process as recited in claim 68, wherein said polymer is polyvinyl chloride.

72. A process as recited in claim 68, further comprising the step of forming a layer of an inner reference material upon said first region of said continuous conducting layer before said step of forming said ion-sensitive membrane.

73. A process as recited in claim 72, wherein said step of forming a layer of an inner reference material comprises the substeps of:

(a) grinding together substantially equal parts of mercury and mercury chloride to obtain a paste;

(b) moistening said paste with a saturated solution of potassium chloride;

(c) saturating the thus-moistened paste with calcium sulfate dihydrate; and

(d) applying said paste to said first region of said continuous conducting layer.

74. An improved ion-sensitive electrode comprising:

(a) a substrate having a substrate surface;

(b) a conductor bonded to said substrate, said conductor having first and second regions, with at least said first region being formed as a conducting layer on said substrate surface;

(c) an ion-sensitive membrane bonded to said substrate and to at least a portion of said conductor, said membrane including a continuous membrane layer covering said first region of said conductor and portions of said substrate surface contiguous to said first region of said conductor;

(d) output means connected to said second region of said conductor for interconnecting said electrode with a utilization device; and

(e) fluid-tight sealing means bonded to said substrate, to said conductor, and to said output means, said fluid-tight sealing means covering at least said second region of said conductor and portions of said substrate and said output means adajacent said second region of said conductor.

75. An electrode as recited in claim 74, wherein said ion-sensitive membrane is formed from an ion-sensitive glass.

76. An electrode as recited in claim 75, wherein said ion-sensitive glass is a pH-sensitive glass.

77. An electrode as recited in claim 74, wherein said conductor includes a plurality of metallic layers formed in succession on said substrate.

78. An electrode as recited in claim 77, wherein said plurality of metallic layers are formed by a vapor deposition process.

79. An electrode as recited in claim 74, wherein said output means includes an active device chip bonded to said substrate, said active device chip having an input terminal and at least one output terminal;

interconnecting lead means connected to said second region of said cconductor and said input terminal of said active device chip; and

, output lead means connected to said output terminal of said active device chip for interconnecting said electrode with a utilization device; and

, wherein said fluid-tight sealing means is also bonded to and covers said active device chip, said interconnecting means, and a portion of said output lead means immediately adjacent said output terminal of said active device chip.

80. An electrode as recited in claim 79, wherein said active device chip includes a field effect transistor.

81. An electrode as recited in claim 74, wherein said output means includes an output lead connected to said second region of said conductor for interconnecting said electrode with a utilization device;

and, wherein said fluid-tight sealing means is bonded to and covers a portion of said output lead immediately adjacent said second region of said conductor.

82. An electrode as recited in claim 74, wherein said fluid-tight sealing means comprises:

a body having a cavity therein, said substrate being received in said cavity so that said body covers at least said second region of said conductor and portions of said substrate adjacent said second region; and

, a potting material contained within and filling said cavity.

83. An electrode as recited in claim 74, wherein said ion-sensitive membrane is formed from a polymer loaded with an ion-exchanging material.

84. An electrode as recited in claim 83, wherein said polymer is polyvinyl chloride.

85. An electrode as recited in claim 83, wherein said ion-exchanging material is calcium didecylphosphate.

86. An electrode as recited in claim 83, wherein said ion-exchanging material is valinomycin.

87. An electrode as recited in claim 83, wherein said electrode further comprises a layer of inner reference material interposed between said first region of said conductor and said ion-sensitive membrane.

88. A process for fabricating an ion-sensitive electrode, said process comprising the steps of:

(a) fabricating a substrate from a substrate material, said substrate having a substrate surface;

(b) forming a continuous conducting layer having a desired configuration on said substrate surface;

(c) forming a continuous ion-sensitive membrane layer on a first region of said continuous conducting layer and portions of said substrate surface contiguous to said first region of said continuous conducting layer;

(d) connecting at least one lead to a second region of said continuous conducting layer; and

(e) forming a fluid-tight seal over at least said second second region of said continuous conducting layer, portions of said substrate surface contiguous to said second region, and a portion of said lead adjacent said second region.

89. A process as recited in claim 88, wherein said continuous conducting layer is formed by a thin-film, vapor deposition subprocess.

90. A process as recited in claim 88, wherein said continuous conducting layer is formed by a thick-film screening subprocess.

91. A process as recited in claim 88, wherein said ion-sensitive membrane layer is formed by a thick-film screening subprocess.

92. A process as recited in claim 88, further comprising the steps of:

(a) bonding an active device chip to said substrate surface, said active device chip including an input terminal and at least one output terminal;

(b) bonding a first lead to said second region of said conducting layer and to said input terminal of said active device chip;

(c) connecting a second lead to said output terminal of said active device chip; and

(d) forming said fluid-tight seal additionally over said first lead, said active device chip, and a portion of said second lead adjacent said active device chip.

93. A process as recited in claim 88, wherein said ion-sensitive membrane layer is formed by dipping said substrate into a solution including a polymer, an ion-exchanging material, and a solvent therefor so that said solution covers at least said first region of said continuous conducting layer, and removing said substrate from said solution and allowing said solvent to evaporate.

94. A process as recited in claim 93, wherein said membrane is sensitive to calcium ions and said ion-exchanging material is calcium didecylphosphate.

95. A process as recited in claim 93, wherein said polymer is polyvinyl chloride.

96. A process as recited in claim 93, further comprising the step of forming a layer of an inner reference material upon said first region of said continuous conducting layer before said step of forming said ion-sensitive membrane layer.