Electricity: circuit makers and breakers – Liquid contact – Plural switches
Reexamination Certificate
2002-06-21
2004-09-28
Luebke, Renee (Department: 2833)
Electricity: circuit makers and breakers
Liquid contact
Plural switches
C200S191000, C200S214000, C200S233000, C337S021000, C337S326000
Reexamination Certificate
active
06797901
ABSTRACT:
BACKGROUND OF THE INVENTION
Published Japanese Patent Application No. S47-21645 discloses an example of a switch device for electrically switching solid electrodes by means of a conductive fluid. In this switch device, a conductive fluid composed of a liquid such as mercury is disposed movably inside a cylinder. The switch device is designed so that the conductive fluid is moved to one side by a pressure differential in a gas provided on both sides of the conductive fluid. When the conductive fluid moves, it touches electrodes that extend into the interior of the cylinder and forms an electrical connection between the electrodes. A drawback to this structure, however, is that the electrical connection characteristics of the switch device deteriorate as a result of the surfaces of the electrodes being modified over time by intermittent contact with the conductive fluid.
U.S. Pat. No. 6,323,447 of Kondoh et al., assigned to the assignees of this disclosure and incorporated herein by reference, discloses a switch device structure that solves the above-mentioned problem. In this switch device structure, the electrical path is selectively changed from a connected state to a disconnected state by a conductive fluid such as mercury. However, the electrodes remain in constant contact with part of the conductive fluid, and the connected or disconnected state of the electrical path is determined by whether the conductive fluid exists as a single entity (connected state) or is separated into two or more conductive fluid portions (disconnected state). This eliminates the problem of poor connections that was a disadvantage of the switch device disclosed in published Japanese Patent Application No. S47-21645.
In the switch device disclosed in U.S. Pat. No. 6,323,447, the material of the wall of the passage in which the conductive fluid is located has a low wettability with respect to the conductive fluid. Moreover, conventional manufacturing methods, such as anisotropically etching silicon, other types of dry etching, or a method such as applying a dry film, for forming the passage form the passage with a triangular, square, rectangular, trapezoidal or semicircular cross-sectional shape.
FIG. 1
is a cross-sectional view of the passage of a typical prior art switch device. The passage
510
is formed in the silicon substrate by anisotropic etching. This design was proposed by J. Simon et. al. in 6 J. MICROELECTROMECHANICAL SYS, 206-216 (September 1997). The passage
510
has a triangular cross-sectional shape. The surface tension of the conductive fluid
520
causes the mercury to accumulate in the middle the passage, leaving gaps between the conductive fluid and the corners of the passage. Such gaps allow the non-conductive fluid to leak from the high-pressure side to the low-pressure side during operation of the switch device, which reduces the ability of the non-conductive fluid to move the conductive fluid. The effectiveness of the non-conductive fluid to move the conductive fluid can be increased by increasing the capacity of the device, such as a heater, that increases the pressure in the high-pressure side. However, when a heater is used as the pressure increasing device, increasing its capacity requires that the heater have a larger surface area or that it dissipate greater power. This not only increases the size of the switch device and increases the power consumption, but also towers the degree of freedom in design.
SUMMARY OF THE INVENTION
The invention solves the above problems, and provides a switch device that is more compact and uses less power than the conventional switch devices described above. The improvements are accomplished by reducing the leakage of the non-conductive fluid from the high-pressure side to the low-pressure side during operation of the switch device.
The invention provides a switch device comprising a pair of cavities, an elongate passage, a non-conductive fluid having a high electrical resistance, a conductive fluid having a high electrical conductivity and an electrical path. The passage is in fluid communication with the cavities and has a substantially elliptical cross-section over at least part of its length. The non-conductive fluid is disposed in each of the cavities. The conductive fluid is located in the passage. The electrical path is changeable between a connected state and a disconnected state by the non-conductive fluid separating the conductive fluid in the passage into non-contiguous conductive fluid portions.
The invention additionally provides a switch device comprising a pair of cavities, an elongate passage, a non-conductive fluid having a high electrical resistance, a conductive fluid having a high electrical conductivity and a wettable material. The passage is in fluid communication with the pair of cavities. The passage has a cross-sectional shape that, over at least a portion of the length of the passage, includes a corner. The non-conductive fluid is located in each of the pair of cavities. The conductive fluid is located in the passage in contact with the non-conductive fluid from the each of the cavities. The wettable material is wettable by the conductive fluid, is in contact with the conductive fluid and is located in at least part of the portion of the length of the passage where the cross-sectional shape includes the corner.
Finally, the invention provides a method of making a switch device. In the method, a pair of plates, a non-conductive fluid having a high electrical resistance and a conductive fluid having a high electrical conductivity are provided. A pair of cavities and a passage that allows the pair of cavities to communicate are formed in at least one of the plates The passage has a cross-sectional shape that includes a corner over at least part of its length. The plates are mated. A portion of the non-conductive fluid is placed in each of the cavities. The conductive fluid is placed in the passage in contact with the portion of the non-conductive fluid in each of the cavities. A wettable film that is wettable by the conductive fluid is formed on at least one of the plates. The wettable film is located adjacent the corner of the cross-sectional shape and extends widthways and lengthways in the passage when the pair of plates is mated.
REFERENCES:
patent: 3249772 (1966-05-01), Lindberg
patent: 3646490 (1972-02-01), Bitko
patent: 4371753 (1983-02-01), Graf
patent: 5726404 (1998-03-01), Brody
patent: 6323447 (2001-11-01), Kondoh et al.
patent: 1179829 (2002-02-01), None
patent: 699243 (1930-12-01), None
patent: 51-1309 (1976-01-01), None
patent: 09-161640 (1996-06-01), None
Simon, Jonathan et al., “A Micromechanical Relay with a THermally-Driven Mercury Micro-Drop”, Proceedings of Wordshop on Micro Electro Mechanical System, Feb. 11-15, 1996, pp. 515-520.
Simon, Jonathan et al., “A Liquid-Filled Micrortelay with a Moving Mercury Microdrop”, Journal of Microelectromechanical Systems, vol. 6, No. 3, Sep. 1997, pp. 208-216.
Kondoh You
Saito Mitsuchika
Agilent Technologie,s Inc.
Luebke Renee
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