Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Utilizing conductive liquid
Reexamination Certificate
2002-04-30
2003-11-11
Nguyen, Tuyen T. (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Utilizing conductive liquid
C200S181000
Reexamination Certificate
active
06646527
ABSTRACT:
BACKGROUND OF THE INVENTION
RF step attenuators are an important part of many general purpose electronic instruments such as spectrum analyzers, network analyzers, S-parameter test sets, signal generators, sweep generators, and high frequency oscilloscopes, just to name a few. Special purpose test sets, such as those used to test wireless communications equipment are also important users of RF step attenuators. Decades ago an RF step attenuator was a manually operated device: the human hand generally turned a knob. With the advent of automated test systems under computer control, and the more recent advent of automatic test equipment that has its own internal processor, has a sophisticated repertoire of testing abilities, and has extensive instrument-to-instrument communication abilities, the need for attenuators that are electrically controlled has steadily grown, and continues to do so. The increases in performance, both in accuracy and in higher frequencies of operation, have placed additional demands upon the nature of the desired attenuators. Furthermore, stand-alone instrument grade programmable (solenoid operated) step attenuators usable in the microwave region are simply too big and too costly for many of today's designs, where much of the circuitry is integrated.
One prior art response to this situation is represented by the A150 line of ultra-miniature attenuator relays from Teledyne (www.teledynerelays.com—12525 Daphne Avenue, Hawthorne, Calif., 90250). They are small, approximately three-eighths by seven-sixteenths of an inch in length and width by less than a third of an inch in height. They are usable to 3 GHz, have an internal matched thin film attenuator (pad) available in Pi, T or L sections, and are available in a variety of attenuations of from 1 dB to 20 dB. This family of relays provides the “step” in attenuation by replacing the pad with a length of conductor. The mechanical arrangement for doing this is set out in U.S. Pat. No. 5,315,723, issued May 24, 1994 and entitled ATTENUATOR RELAY. It does not appear that the length of conductor that replaces the pad is a section of genuine controlled impedance transmission line.
FIG. 1
is a generalized representation of a prior art step attenuator relay
1
, such as the A150 attenuator relay. An RF input
2
is coupled to the moving pole of a SPDT switch
4
, and an RF output
3
is taken from the moving pole of a SPDT switch
5
. Switches
4
and
5
are operated together by the solenoid of the relay (not shown), with the effect that either an attenuator section
6
or a conductor
7
is connected between the RF input
2
and the RF output
3
. It is not so much that this arrangement is defective, it works up to some upper frequency where geometry begins to significantly influence circuit behavior. At higher frequencies the stray coupling capacitances
10
and
11
(which are around one hundred femto farads) allow conductor
7
to begin to shunt the attenuator
6
, and RF currents will flow around the attenuator
6
, driven by the voltage drop across the attenuator itself. There are minor stray reactances within the conductor
7
, which we have indicated in a very general way by the series inductances
8
and the shunt capacitance
9
. At higher frequencies the stray coupling capacitances
10
and
11
combine with the stray reactances
8
and
9
to form a resonant circuit that poisons the attenuation inserted by the relay
1
. In the case of the A150 this happens at around 4 GHz.
Recent developments have occurred in the field of very small switches having liquid moving metal-to-metal contacts and that are operated by an electrical impulse. That is, they are actually small latching relays that individually are SPST or SPDT, but which can be combined to form other switching topologies, such as DPDT. (Henceforth we shall, as is becoming customary, refer to such a switch as a Liquid Metal Micro Switch, or LIMMS.) With reference to
FIGS. 2-5
, 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 a high performance high frequency step attenuator using a collection of such relays.
Refer now to
FIG. 2A
, 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
18
in which there are two small movable distended droplets (
23
,
24
) of a conductive liquid metal, such as mercury. The channel
18
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
16
and
17
, within which are respective heaters
14
and
15
, each of which is surrounded by a respective captive atmosphere (
21
,
22
) of an inert gas, such as CO
2
. Cavity
16
is coupled to the channel
18
by a small passage
19
, opening into the channel
18
at a location about one third or one fourth the length of the channel from its end. A similar passage
20
likewise connects cavity
17
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 the long mercury droplet, forcing the detached portion 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 A through the middle of the heaters
14
and
15
. New elements in this view are the bottom substrate
13
, 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
25
of sealing adhesive bonds the cover block
12
to the substrate
13
, which also makes the cavities
16
and
17
, passages
19
and
20
, and the channel
18
, all gas tight (and also mercury proof, as well!). Layer
25
may be of a material called CYTOP (a registered trademark of Ashai Glass Co., and available from Bellex International Corp., of Wilmington, Del.). Also newly visible are vias
26
-
29
which, besides being gas tight, pass through the substrate
13
to afford electrical connections to the ends of the heaters
14
and
15
. So, by applying a voltage between vias
26
and
27
, heater
14
can be made to become very hot very quickly. That in turn, causes the region of gas
21
to expand through passage
19
and begin to force long mercury droplet
23
to separate, as is shown in FIG.
3
. At this time, and also before heater
14
began to heat, long mercury droplet
23
physically bridges and electrically connects contact vias
30
and
31
, after the fashion shown in FIG.
2
C. Contact via
32
is at this time in physical and electrical contact with the small mercury droplet
24
, but because of the gap between droplets
23
and
24
, is not electrically connected to via
31
.
Refer now to
FIG. 4A
, and observe that the separation into two parts of what used to be long mercury droplet
23
has been accomplished by the heated gas
21
, and that the right-hand portion (and major part of) the separated mercury has joined what used to be smaller droplet
24
. Now droplet
24
is the larger drople
Dascher David J
Dove Lewis R
Lindsey John R
Agilent Technologie,s Inc.
Miller Edward L.
Nguyen Tuyen T.
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