Electricity: circuit makers and breakers – Liquid contact
Reexamination Certificate
2000-01-08
2001-11-27
Bradley, Paula (Department: 2832)
Electricity: circuit makers and breakers
Liquid contact
C200S214000
Reexamination Certificate
active
06323447
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrical contact breaker switch, an integrated electrical contact breaker switch, and an electrical contact switching method in which the switching between solid electrodes is performed mechanically by means of a conductive fluid, and more particularly relates to a breaker switch, such as mechanical contact type microrelays and microswitches of high reliability, and to an integrated breaker switch or switching method thereof.
BACKGROUND OF THE INVENTION
The typical compact, mechanical contact type of relay used in the past was a lead relay. A lead relay is furnished with a lead switch, in which two leads composed of a magnetic alloy are contained, along with an inert gas, inside a miniature glass vessel. A coil for an electromagnetic drive is wound around the lead switch, and the two leads are installed within the glass vessel as either contacting or non-contacting. Usually with this type of lead relay, in a non-drive state, current does not flow through the coil, and the ends of the leads repel each other and are not in contact. In the drive state current, current flows through the coil, and the ends of the leads attract each other and make contact.
Lead relays include dry lead relays and wet lead relays. Usually with a dry lead relay, the ends (contacts) of the leads are composed of silver, tungsten, rhodium, or an alloy containing any of these, and the surfaces of the contacts are plated with rhodium, gold, or the like. The contact resistance is high at the contacts of a dry lead relay, and there is also considerable wear at the contacts. Since reliability is diminished if the contact resistance is high at the contacts or if there is considerable wear at the contacts, there have been various attempts to treat the surface of these contacts.
Reliability of the contacts may be enhanced by the use of mercury with a wet lead relay. Specifically, by covering the contact surfaces of the leads with mercury and by using capillary action, the contact resistance at the contacts is decreased and the wear of the contacts is reduced, which results in improved reliability.
In addition, because the switching action of the leads is accompanied by mechanical fatigue due to flexing, the leads may begin to malfunction after some years of use, which also diminishes reliability. Japanese Patent Publication SHO 36-18575 and Japanese Laid-Open Patent Applications SHO 47-21645 and HEI 9-161640 disclose techniques for reducing this mechanical fatigue of the leads, lowering the contact resistance at the contacts, and making the relay more compact overall.
In these publications, the switching mechanism is structured such that a plurality of electrodes are exposed at specific locations along the inner walls of a slender sealed channel that is electrically insulating. This channel is filled with a small volume of an electrically conductive liquid to form a short liquid column. When two electrodes are to be electrically closed, the liquid column is moved to a location where it is simultaneously in contact with both electrodes. When the two electrodes are to be opened, the liquid column is moved to a location where it is not in contact with both electrodes at the same time.
To move the liquid column, Japanese Laid-Open Patent Application SHO 47-21645 discloses creating a pressure differential across the liquid column. The pressure differential is created by varying the volume of a gas compartment located on either side of the liquid column, such as with a diaphragm. Japanese Patent Publication SHO 36-18575 and Japanese Laid-Open Patent Application HEI 9-161640 disclose creating a pressure differential across the liquid column by providing the gas compartment with a heater. The heater heats the gas in the gas compartment located on one side of the liquid column.
The technology disclosed in Japanese Laid-Open Patent Application 9-161640 (relating to a microrelay element) can also be applied to an integrated circuit. Also, as the technology continues to develop, this type of relay may be made even more compact and faster, as disclosed by J. Simon, et al. (A Liquid-Filled Microrelay with a Moving Mercury Drop, Journal of Microelectromechanical Systems, Vol. 6, No. 3, September 1997). Furthermore, this type of relay may no longer be gravity dependent (attitude dependent), the mercury contacts may have a much longer service life, reliability may be enhanced, and even environmental pollution during manufacturing may be kept to a minimum.
FIG. 1
is a plan view of the layout of the latch-type thermodrive microrelay elements disclosed in Japanese Laid-Open Patent Application HEI 9-161640. The microrelay elements are formed in a specific region of a semiconductor substrate
91
and include an active reservoir
921
, a passive reservoir
922
, and a channel
93
. The active reservoir
921
and passive reservoir
922
are each provided with a plurality of cantilevered heaters
941
and
942
, and the active reservoir
921
and passive reservoir
922
are connected by the channel
93
. In
FIG. 1
, a heater support stand is provided under the heaters
941
and
942
.
A microchannel region
931
, having a smaller diameter than the channel
93
, is formed at a location midway along the channel
93
. A first channel region
932
is formed on the active reservoir
921
side of the microchannel region
931
, while a second channel region
933
is formed on the passive reservoir
922
side. The first channel region
932
is connected to the active reservoir
921
via a first narrow channel
934
, and the second channel region
933
is connected to the passive reservoir
922
via a second narrow channel
935
. First signal electrodes
951
and
952
are exposed in the first channel region
932
, and second signal electrodes
954
and
955
are exposed in the second channel region
933
. The channel portion consisting of the microchannel region
931
, the first channel region
932
, and the second channel region
933
is filled with a liquid metal
96
, which serves as a conductive fluid column.
With the microrelay in
FIG. 1
, the first signal electrodes
951
and
952
can be “opened” and the second signal electrodes
954
and
955
can be “closed” by heating the heater
941
to raise the internal pressure of the active reservoir
921
. This internal pressure rise of the active reservoir
921
causes the liquid metal
96
to move to the second channel region
933
. Similarly, the first signal electrodes
951
and
952
can be “closed” and the second signal electrodes
954
and
955
can be “opened” by heating the heater
942
to raise the internal pressure of the passive reservoir
922
. This internal pressure rise of the passive reservoir
922
causes the liquid metal
96
to move to the first channel region
932
.
With a conventional microrelay as shown in
FIG. 1
, the relay is “closed” by moving a column of conductive fluid so that the fluid is simultaneously in contact with two electrode components. The relay is “opened” by moving the column so that it is not in contact with the two electrode components at the same time. The electrical switching point corresponds to the contact between the conductive fluid and the electrode components of the solid electrodes.
With a microrelay element having a structure as shown in
FIG. 1
, there is the danger that the surfaces of the electrodes will become rough or that the electrode surfaces will be corroded by components of the gas inside the channel
93
in the course of switching the first signal electrodes
951
and
952
or the second signal electrodes
954
and
955
. As a result, the switching action may be unstable and reliability may diminish.
SUMMARY OF THE INVENTION
Deterioration due to corrosion of the electrode component surfaces, such as caused by chemical reactions with components of the gas within the cavities, can be eliminated. Furthermore, the voltage between the electrode components can be varied if the switching of the relay is performed by modifying the form of the conductive fluid. The conductive fl
Ichimura Yoshikatsu
Kondoh You
Saito Mitsuchika
Agilent Technologie,s Inc.
Bradley Paula
Nguyen Nhung
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