Micro machine switch

Details Micro machine switch Micro machine switch

2002-05-16

2004-08-31

Young, Brian (Department: 2819)

Wave transmission lines and networks

Long line elements and components

Switch

C333S105000

Reexamination Certificate

active

06784769

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a micromachine switch used in a milliwave band to microwave band.
BACKGROUND ART
Switch devices such as a PIN diode switch, HEMT switch, micromachine switch, and the like are used in a milliwave band to microwave band. Of these switches, the micromachine switch is characterized in that the loss is smaller than that of the other devices, and a compact high-integrated switch can be easily realized.
FIG. 21
is a perspective view showing the structure of a conventional micromachine switch.
FIG. 22
is a plan view of the micromachine switch shown in FIG.
21
.
A micromachine switch
101
is constructed by a switch movable element
111
, support means
105
, and switch electrode
104
. The micromachine switch
101
is formed on a dielectric substrate
102
together with two RF microstrip lines
121
a
and
121
b
. A GND plate
103
is disposed on the lower surface of the dielectric substrate
102
.
The microstrip lines
121
a
and
121
b
are closely disposed apart from each other at a gap G. The switch electrode
104
is disposed between the microstrip lines
121
a
and
121
b
on the dielectric substrate
102
. The switch electrode
104
is formed to have a height lower than that of each of the microstrip lines
121
a
and
121
b.
The switch movable element
111
is arranged above the switch electrode
104
. A capacitor structure is formed by the switch electrode
104
and switch movable element
111
.
As shown in
FIG. 22
, since a length L of the switch movable element
111
is larger than the gap G, two ends of the switch movable element
111
oppose the end portions of the microstrip lines
121
a
and
121
b
, respectively. The switch movable element
111
is formed to have a width g equal to a width W of each of the microstrip lines
121
a
and
121
b.
The switch movable element
111
is cantilevered on the support means
105
fixed on the dielectric substrate
102
.
As shown in
FIG. 21
, the switch movable element
111
is generally arranged above the microstrip lines
121
a
and
121
b
. With this structure, since the switch movable element
111
is not in contact with the microstrip lines
121
a
and
121
b
, the micromachine switch
101
is in an OFF state. At this time, a little high-frequency energy is transmitted from the microstrip line
121
a
to the microstrip line
121
b.
When, however, a control voltage is applied to the switch electrode
104
, the switch movable element
111
is pulled down by an electrostatic force. When the switch movable element
111
is brought into contact with the microstrip lines
121
a
and
121
b
, the switch movable element
111
is set in an ON state. At this time, the high-frequency energy from the microstrip line
121
a
is transmitted to the microstrip line
121
b
through the switch movable element
111
.
As described above, the two ends of the switch movable element
111
oppose the microstrip lines
121
a
and
121
b
, respectively. Accordingly, the capacitor structures are also formed between the switch movable element
111
and the microstrip lines
121
a
and
121
b.
This makes the capacitive coupling between the switch movable element
111
and microstrip lines
121
a
and
121
b
so that the high-frequency energy from the microstrip line
121
a
leaks out into the microstrip line
121
b
even if the micromachine switch
101
is in the OFF state. That is, in the conventional micromachine switch
101
, an OFF isolation characteristic is poor.
A capacitance between the switch movable element
111
and the microstrip lines
121
a
and
121
b
is proportional to the opposing area between them. Accordingly, an increase in opposing area increases energy leakage, thereby degrading the isolation characteristic. On the contrary, a decrease in opposing area may improve the isolation characteristic. Therefore, the isolation characteristic can be improved by decreasing the width g of the switch movable element
111
.
However, a high-frequency characteristic impedance of a line is related to the surface area of the line, and a decrease in width of the line increases the characteristic impedance. Thus, if the width g of the switch movable element
111
decreases, the characteristic impedance on the gap G increases in the ON state of the micromachine switch
111
.
High-frequency energy reflection occurs at a discontinuous portion in the line. An increase in characteristic impedance on the gap G results in impedance mismatching. Thus, since the reflection increases in the ON state of the micromachine switch
101
, the ON reflection characteristics degrades.
For example, the microwave switching circuit requires the isolation characteristic of approximately 15 dB or more and the reflection characteristics of approximately −20 dB or less.
The present invention has been made to solve the above problem, and has as its object to suppress the degradation of the ON reflection characteristic of the micromachine switch and improve the OFF isolation characteristic.
DISCLOSURE OF INVENTION
In order to achieve the above object, the present invention comprises at least two distributed constant lines disposed close to each other, a movable element arranged above the distributed constant lines such that distal end portions of the movable element oppose the distributed constant lines, respectively, and connecting the distributed constant lines to each other in a high-frequency manner upon contacting the distributed constant lines, and driving means for displacing the movable element by an electrostatic force to bring the movable element into contact with the distributed constant lines, wherein the movable element has at least two projections formed by notching an overlap portion of the movable element which is located on at least one distributed constant line side, and the projections oppose a corresponding distributed constant line. This decreases the opposing area between the movable element and the distributed constant line, thereby reducing the capacitive coupling of the movable element and distributed constant line without decreasing the width of the movable element. When the projection has a width (the length in the direction parallel to the widthwise direction of the distributed constant lines) 1
(where n is a real number larger than 1) the width of the movable element main body (a portion of the movable element except for the projections), the projection has a high-frequency characteristic impedance much lower than n times the characteristic impedance of the movable element main body. On the other hand, the characteristic impedance of an end portion of the movable element is the synthetic impedance of the projections formed in parallel. Therefore, even the end portion of the movable element can obtain the characteristic impedance almost equal to that of the movable element main body, thereby suppressing the degradation of an ON reflection characteristic of the micromachine switch and improving an OFF isolation characteristic.
In the present invention, movable element main body serving as a portion of the movable element except for projections has a width serving as a length in a direction parallel to the widthwise direction of the distributed constant lines to be equal to a width of each of the distributed constant lines, and, a portion of the overlap portion of the movable element except for two ends in the movable element is notched. With this structure, the characteristic impedance on a gap becomes almost equal to that of each of the distributed constant lines. Thus, the degradation of an ON reflection characteristic of the micromachine switch can be prevented and an OFF isolation characteristic can be improved.
In the present invention, movable element main body serving as a portion of the movable element except for projections has a width serving as a length in a direction parallel to the widthwise direction of the distributed constant lines to be smaller than a width of each of the distributed constant lines, and a portion of the overlap portion of the movable element except for t

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