Conductivity sensor and manufacturing method therefor

A contacting-type conductivity sensor includes a plurality of electrodes disposed on a distal surface of a substrate. The substrate includes a plurality of vias through which electrical interconnection to the electrodes is accomplished. The conductivity sensor can employ two or four electrodes and may have a temperature sensitive element disposed on the distal surface. The electrodes may be patterned or otherwise deposited using semiconductor processing techniques.

BACKGROUND OF THE INVENTION

Conductivity measurement sensors are well known in the art and are used to measure the conductivity of a fluid, such as a liquid or a dispersion of solids suspended in a liquid. Conductivity sensors are often used to investigate the properties of electrolytes in solution, such as the degree of dissociation, the formation of chemical complexes, and the hydrolysis. The conductivity of a fluid may also be used to measure a wide variety of other parameters, such as the amount of contaminants in drinking water and a measure of chemical concentrations in industrial processes. Applications such as these involve the determination of conductivities in many physical environments.

The units of conductivity are Siemens/cm, which are identical to the older unit of mhos/cm. Conductivity measurements cover a wide range of solution conductivity from pure water at less than 1×10−7S/cm to values in excess of 1 S/cm for concentrated solutions.

One conductivity measurement technique includes contacting a solution with electrically conducting electrodes. For example, one contacting conductivity measurement technique employs a sensor with two metal or graphite electrodes in contact with the electrolyte solution. An alternating current (AC) voltage is applied to the electrodes by the conductivity analyzer, and the resulting AC current that flows between the electrodes is used to determine the conductance. Contacting-type conductivity sensors generally employ two, or sometimes four, contacting electrodes, which physically contact the sample solution. In the case of four-electrode contacting sensors, the four-electrodes are exposed to the sample solution and a current is passed through one pair of electrodes. A voltage change between the other pair of electrodes is then measured. Based on the current and voltage, the conductivity of the liquid is calculated. Traditionally, contacting-type conductivity sensors, such as two or four-electrode sensors, are made by inserting conductive rods, (made of stainless steel, titanium, graphite, etc.) in a plastic tube, which rods are then sealed with epoxy along their length. The cross section of one end of the plastic tube is then used to expose the electrodes to the sample solution.FIG. 1Ais a diagrammatic view of a four-electrode contacting-type conductivity sensor10in accordance with the prior art. Sensor10is coupled to a suitable conductivity analyzer12. Distal end14of sensor10exposes distal ends16of conductive rods18to a sample solution disposed proximate distal end14.FIG. 1Bis a bottom plan view of sensor10illustrating distal ends16of rods18.

Recently, contacting-type conductivity sensors, such as two and four-electrode conductivity sensors have been made by using semiconductor-like, planar manufacturing technologies. The electrodes are deposited on a passivated silicon wafer through suitable processing techniques, such as thin/thick film technology. Conductivity sensors manufactured in accordance with such semiconductor processing techniques can be mass-produced resulting in reduced size and cost of such sensors. However, the reduction in size of semiconductor-based conductivity sensors creates other manufacturing difficulties. Providing a semiconductor-based contacting-type conductivity sensor design that facilitated low-cost semiconductor-based manufacturing techniques would further benefit the art.

SUMMARY OF THE INVENTION

A contacting-type conductivity sensor includes a plurality of electrodes disposed on a distal surface of a substrate. The substrate includes a plurality of vias through which electrical interconnection to the electrodes is accomplished. The conductivity sensor can employ two or four electrodes and may have a temperature sensitive element disposed on the distal surface. The electrodes may be patterned or otherwise deposited using semiconductor processing techniques.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 2Ais a perspective view of a substrate with which embodiments of the present invention are particularly useful. Substrate20is illustrated in the form of a disc, but can take any suitable form. Generally, however, in order to facilitate semiconductor processing techniques and manufacturing methods, substrate20is relatively flat and thin. Substrate20can be formed out of any material that is amenable to semiconductor processing techniques and manufacturing methods. As such, substrate20can be formed of any suitable ceramic, glass, or combination thereof. Substrate20is substantially non-conductive in comparison to metal conductors, and inorganic. Suitable examples of materials for substrate20include silicon, zirconium oxide, aluminum oxide, Pyrex, or any other suitable material. In accordance with an embodiment of the present invention, substrate20includes a number of through holes or vias22. Each of vias22extend from fluid contacting, distal surface24to interior, proximal surface26.

FIG. 2Bis a cross sectional view of substrate20.FIG. 2Billustrates holes or vias22extending from distal, sample contacting surface24to proximal surface26. Vias22can be formed in accordance with any suitable techniques including semiconductor-processing techniques including etching processes, such as wet etching and/or dry etching such as reactive ion etching (RIE). Moreover, the vias can be generated using other suitable techniques including mechanical/laser drilling.

FIG. 2Cis a cross sectional view of substrate20where vias22are filled with a conductive metal. Each of vias22is at least partially filled with conductive metal28extending through the entire length of the via from surface24to surface26. Conductive metal28is bonded directly to the inner diameter surfaces of vias22using suitable techniques forming a hermetic seal. In one example, the metal can be deposited using electron-beam vacuum deposition. However, other semiconductor processes that transfer materials onto a semiconductor material can be used such as physical vapor deposition (PVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE) and atomic layer deposition (ALD). WhileFIG. 2Cillustrates vias22filled completely by metal28, it is contemplated that a portion of the via proximate the inner diameter of the via could be filled with metal and then the remaining portion, (inner diameter of the metal) could be later filled with any suitable inorganic sealing material. The deposition of metal28within vias22thus generates a “metalized” via extending between distal surface24and proximal surface26thereby generating an electrical path between the two surfaces along the via. The metalized via may have metal28completely filling the via, or metal28may only partially fill the via as long as metal28extends from surface24to surface26. If metal28partially fills a via22, then a suitable sealing agent, such as a glass frit, can be used to generate the final hermetic seal within vias22.

FIG. 2Dis a diagrammatic view of substrate20with electrodes30deposited proximate and in contact with metal28. Electrodes30can be formed of any suitable conductor that is chemically resistant. Examples of such suitable materials include, without limitation, platinum and gold. As with the deposition of metal28, the deposition of electrodes30can be effected using any suitable thin or thick film techniques. Examples include suitable deposition processes such as physical vapor deposition, chemical vapor deposition, electrochemical deposition, molecular beam epitaxy and automatic layer deposition. Moreover, electrode material may simply be provided in sheet form and then selectively removed to generate the electrodes. Suitable semiconductor removal processes include etching processes, such as wet etching or dry etching.

FIG. 2Eillustrates substrate20having electrodes30disposed proximate and contacting metal28in vias22. Additionally,FIG. 2Eillustrates a metal transition layer32electrically coupled to proximal ends of metal28at or proximate proximal surface26. Transition layers32facilitate the subsequent attachment of electrical connectors, such as pins or wires. The material selected for transition layers32can be the same as that of metal28, and/or the pins or conductors that will subsequently be attached. Moreover, transition layers32can also be any suitable alloy, or combination of metals, that is able to effectively bond to metal28and the interconnect.

FIG. 2Fis a cross sectional view of a semiconductor-based contacting-type conductivity sensor in accordance with an embodiment of the present invention. Sensor40includes substrate20having a plurality of vias22filled by an electrically conductive metal28. Sensor40includes electrodes30disposed proximate distal surface24of substrate20, which electrodes30are adapted to pass an electrical current through a solution to measure the conductivity of the solution. Pins34are electrically connected to transition layers32. Pins34are thus electrically coupled directly to electrodes30. The design of sensor40provides an inorganic conductivity sensor where the distal surface is hermetically sealed from proximal surface26. It is preferred that every electrode in contact with the sample solution have an electrical interconnect as disclosed with respect to sensor40. Further, additional electrical features, such as a temperature sensor disposed to measure the temperature of the sample solution are also preferably electrically interconnected by virtue of vias through substrate20filled with metal.

FIG. 3is a perspective view of substrate50having vias52extending from distal surface54to proximal surface56.FIG. 3Bis a cross sectional view of substrate50.FIGS. 3A and 3Billustrate substrate50as substantially identical to substrate20described with respect toFIGS. 2A and 2B, and, in fact, they could be the same. However, in order to better describe this additional embodiment, the substrate is provided with reference numeral50.FIG. 3Cillustrates substrate50having a plurality of transition rings58disposed about vias52at distal surface54. Transition rings58are preferably circularly shaped having an inner diameter that is substantially equal to the inner diameter of vias52. The shape of the outer periphery of each of transition rings58can vary.

FIG. 3Dillustrates a plurality of pins60extending through vias52with a surface62of pinhead64in contact with transition rings58. A suitable electrical connection, such as brazing or welding, between pins64and transition rings58generates not only an electrical connection, but an hermetic seal between distal surface54and proximal surface56. Once pins60are suitably attached to substrate50, electrodes66are deposited over, and electrically connected to pins60. Electrodes66can be formed in any suitable shape.

FIG. 3Eillustrates semiconductor-based contacting-type conductivity sensor68having a plurality of pins60extending through substrate52and generating an electrical connection between electrodes66and electronic circuitry (not shown) coupled to pins60. The actual shape and configuration of the electrodes on the distal surface of the contacting-type semiconductor-based sensor can vary significantly.FIG. 4Aillustrates one such arrangement with a first pair of electrodes70disposed adjacent to a second pair of electrodes72.FIG. 4Billustrates yet another exemplary electrode configuration. A first pair of electrodes74is disposed substantially about a second pair of electrodes76. The utilization of a plurality of pairs of electrodes in a four-electrode conductivity sensor provides some advantages over two-electrode conductivity sensors. However, it should be noted that embodiments of the present invention are equally applicable to both two-electrode sensors and four-electrode sensors. Moreover, the utilization of semiconductor processing techniques for the deposition and/or configuration of the electrodes in contact with the sample solution allows for significantly advanced electrode patterning and shaping. For example,FIG. 4Bprovides significantly more geometric complexity thanFIG. 4Awhich, from a bottom plan view, appears similar to four-electrode sensors of the prior art.

It is known that the conductivity of many solutions actually changes with the temperature of the solution. Thus, some conductivity sensors include a temperature sensor to provide an indication of the temperature of the sample solution. In accordance with yet another embodiment of the present invention, a temperature sensitive element80is disposed on the distal surface or the proximal surface of the conductivity. Element80can be constructed from any material that has an electrical property, such as resistance, that changes in relation to temperature, and which is amenable to semiconductor-processing techniques, such as deposition. One particular suitable metal is platinum. Further, electrical interconnects to the temperature-sensitive element on the distal surface of the sensor is are also preferably effected using metal-filled vias as disclosed above.

The substrate can additionally be mounted within a capsule or rod to complete the sensor assembly or it can be embedded or affixed to any other suitable housing. Further still, the use of semiconductor processing techniques allow for various other devices to potentially be located on the same substrate as that used for the conductivity sensor. Thus, additional sensors and/or electronics can be included, as appropriate.