Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Polarity-responsive
Reexamination Certificate
2002-04-24
2003-10-14
Nguyen, Tuyen T. (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Polarity-responsive
C335S047000
Reexamination Certificate
active
06633213
ABSTRACT:
BACKGROUND OF THE INVENTION
Although many semiconductor devices are called “switches,” and although those devices are used in many circuit applications to perform the electrical connection functions of a traditional metal-to-metal moving contact structure, it is still the case that for a variety of reasons (e.g., ability to carry high currents, high break-down voltages, high isolation, operation in an AC circuit, etc.) a genuine traditional switch is the component of choice. Of course, the term “switch” is broader than the simple class of devices that are operated by a human hand or finger, or by some mechanical linkage to an object such as a door, cockpit canopy or a float, and the term includes what are ordinarily called “relays.” A relay is a switch that is (usually) operated by an electrical signal that is converted (e.g., by a magnetic coil) to mechanical motion that operates the switch. Common relays incorporate a spring tension to return the contacts to an un-operated state in the absence of the electrical signal. On the other hand, some relays have actuation mechanisms that transition from one stable state to another stable state, and that stay transitioned in the absence of, or after the removal of, the signal that produced the change in state. Such relays are called “latching” relays.
Among the reasons for preferring a genuine moving contact switch to one of its semiconductor counterparts is the need for preserving the characteristic impedance of a transmission line that must be switched among other components (attenuators, power splitters, etc.), or the need for simple shielding in a less demanding situation of a conductor that is only shielded, but that is not an actual transmission line having a controlled characteristic impedance. “Coaxial switch” is the term usually given to this sort of structure, and various instances of this sort of thing are produced as relays also, in both latching and non-latching versions. True coaxial relays are an exercise in electro-mechanical fidelity to the transmission line that they are to connect to. They are not small, and they are not inexpensive. They wear out, their contacts oxidize or deform, and their behavior can become erratic. But most of all, they are “big” and are unsuitable for use in many applications involving integrated circuitry, including the assembly of integrated system components onto a substrate to form a “hybrid” circuit. We simply can't bring ourselves to use a relay whose volume is ten to even a thousand times that of the circuitry it is supposed to switch, let alone use several such relays!
On the other hand, if a genuine metal-to-metal switching mechanism is small enough, then below some upper frequency it can largely avoid the evils of a temporary (think: “small”) discontinuity or lapse in shielding, even though it is not itself a coaxial structure. This is follows from the well appreciated fact that when the physical size of the departure from ideal geometry is small compared to the shortest wavelength present, then the resulting discontinuity is essentially invisible, or at least tolerable. This is a long way of saying that if we have a genuine switch that is small enough, we may well be able to use it in place of a much larger coaxial switch, even though the small switch is not truly a segment of a transmission line structure. The same goes for shielding, although that is often easier to supply, since it does not have the worry of maintaining a characteristic impedance that is strongly influenced by geometry. And equally as valuable, such a small relay would be of a size that is comparable to, or maybe even a little smaller than, the circuit elements it is to switch among, and the whole works can be fabricated on a substrate as a hybrid. We have just called such a thing a relay, rather than a switch, since at the sizes we are interested in (say, one tenth inch by one tenth inch) it is most unlikely that such a switch would have a bat handle, lever or other mechanical linkage through which it is to be operated. In times past such a relay was fanciful, but that is no longer so.
Recent developments have occurred in the field of very small switches having liquid moving metal-to-metal contacts. With reference to
FIGS. 1-4
, we shall briefly sketch the general idea behind one class of these devices. Having done that, we shall advance to the topic that is most of interest to us, which is a technique for fabricating on a hybrid substrate dense collections of such relays. (Henceforth we shall, as is becoming customary, refer to such a switch as a Liquid Metal Micro Switch, or LIMMS.)
Refer now to
FIG. 1A
, which is a top sectional view of certain elements to be arranged within a cover block
2
of suitable material, such as glass. The cover block
2
has within it a closed-ended channel
1
in which there are two small movable distended droplets (
10
,
11
) of a conductive liquid metal, such as mercury. The channel
1
is relatively small, and appears to the droplets of mercury to be a capillary, so that surface tension plays a large part in determining the behavior of the mercury. One of the droplets is long, and shorts across two adjacent electrical contacts extending into the channel, while the other droplet is short, touching only one electrical contact. There are also two cavities
6
and
7
, within which are respective heaters
4
and
5
, each of which is surrounded by a respective captive atmosphere (
15
,
16
) of an inert gas, such as CO
2
. Cavity
4
is coupled to the channel
1
by a small passage
8
, opening into the channel
1
at a location about one third or one fourth the length of the channel from its end. A similar passage
9
likewise connects cavity
5
to the opposite end of the channel. The idea is that a temperature rise from one of the heaters causes the gas surrounding that heater to expand, which splits and moves a portion of one of the mercury droplets, forcing it to join the short droplet. This forms a complementary physical configuration (or mirror image), with the large droplet now at the other end of the channel. This, in turn, toggles which two of the three electrical contacts are shorted together. After the change the heater is allowed to cool, but surface tension keeps the mercury droplets in their new places until the other heater heats up and drives a portion of the new long droplet back the other way. Since all this is quite small, it can all happen rather quickly; say, on the order of milliseconds.
To continue, then, refer now to
FIG. 1B
, which is a sectional side view of
FIG. 1A
, taken through the middle of the heaters
4
and
5
. New elements in this view are the bottom substrate
3
, which may be of a suitable ceramic material, such as that commonly used in the manufacturing of hybrid circuits having thin film, thick film or silicon die components. A layer
17
of sealing adhesive bonds the cover block
2
to the substrate
3
, which also makes the cavities
4
and
5
, passages
8
and
9
, and the channel
1
, all gas tight (and also mercury proof, as well!). Layer
17
may be of a material called CYTOP (a registered trademark of Ashai Glass Co., and available from Bellex International Corp., of Wilmington, Delaware).
Also newly visible are vias
18
-
21
which, besides being gas tight, pass through the substrate
3
to afford electrical connections to the ends of the heaters
4
and
5
. So, by applying a voltage between vias
18
and
19
, heater
4
can be made to become very hot very quickly. That in turn, causes the region of gas
15
to expand through passage
8
and begin to force long mercury droplet
10
to separate, as is shown in FIG.
2
. At this time, and also before heater
4
began to heat, long mercury droplet
10
physically bridges and electrically connects contact vias
12
and
13
, after the fashion shown in FIG.
1
C. Contact via
14
is at this time in physical and electrical contact with the small mercury droplet
11
, but because of the gap between droplets
10
and
11
, is not electrically connected to via
13
.
R
Agilent Technologie,s Inc.
Miller Edward L.
Nguyen Tuyen T.
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