Micromachine MEMS switch

Details Micromachine MEMS switch Micromachine MEMS switch

2001-05-02

2002-08-13

Pascal, Robert (Department: 2817)

Wave transmission lines and networks

Long line elements and components

Switch

C333S105000, C200S181000

Reexamination Certificate

active

06433657

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. 13
is a perspective view showing the structure of a conventional micromachine switch.
FIG. 14
is a plan view of the micromachine switch shown in FIG.
13
.
A micromachine switch
101
is constructed by a switch movable element
111
, support means
112
, and switch electrode
113
. The micromachine switch
101
is formed on a dielectric substrate
103
together with two RF microstrip lines
102
a
and
102
b
. A GND plate
104
is disposed on the lower surface of the dielectric substrate
103
.
The microstrip lines
102
a
and
102
b
are closely disposed apart from each other at a gap G. The switch electrode
113
is disposed between the microstrip lines
102
a
and
102
b
on the dielectric substrate
103
. The switch electrode
113
is formed to have a height lower than that of each of the microstrip lines
102
a
and
102
b.
The switch movable element
111
is arranged above the switch electrode
113
. A capacitor structure is formed by the switch electrode
113
and switch movable element
111
.
As shown in
FIG. 14
, 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
102
a
and
102
b
, respectively. The switch movable element
111
is formed to have a width equal to the width W of each of the microstrip lines
102
a
and
102
b.
The switch movable element
111
is cantilevered on the support means
112
fixed on the dielectric substrate
103
.
As shown in
FIG. 13
, the switch movable element
111
is generally arranged above the microstrip lines
102
a
and
102
b
. With this structure, since the switch movable element
111
is not in contact with the microstrip lines
102
a
and
102
b
, the micromachine switch
101
is in an OFF state. At this time, a little high-frequency energy is transmitted from the microstrip line
102
a
to the microstrip line
102
b.
When, however, a control voltage is applied to he switch electrode
113
, 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
102
a
and
102
b
, the switch movable element
111
is set in an ON state. At this time, the high-frequency energy from the microstrip line
102
a
is transmitted to the microstrip line
102
b
through the switch movable element
111
.
As described above, the two ends of the switch movable element
111
oppose the microstrip lines
102
a
and
102
b
, respectively. Accordingly, the capacitor structures are also formed between the switch movable element
111
and the microstrip lines
102
a
and
102
b.
This makes the capacitive coupling between the switch movable element
111
and microstrip lines
102
a
and
102
b
so that the high-frequency energy from the microstrip line
102
a
leaks out into the microstrip line
102
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.
In the microwave switching circuit, for example, the isolation of approximately 15 dB or more is required.
The present invention has been made to solve the above problem, and has as its object to improve the OFF isolation characteristic of the micromachine switch.
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 so as to oppose the distributed constant lines 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 includes a projection formed by notching at least one end of an edge of the movable element which is located on at least one distributed constant line side, and a width of the projection serving as a length in a direction parallel to the widthwise direction of the distributed constant lines is smaller than a width of each of the distributed constant lines. That is, at least one end of the movable element is notched to form the projection having the width (the length in the direction parallel to the widthwise direction of the distributed constant lines) smaller than that of the distributed constant line, and the projection is made to oppose the distributed constant line. This decreases the opposing area between the movable element and the distributed constant line, thereby reducing the capacitive coupling of them. Therefore, the OFF isolation characteristic of the micromachine switch can be improved. In addition, since the width of the movable element on the gap between the distributed constant lines becomes larger as compared to the case in which a movable element having the rectangular shape and the width smaller than that of the distributed constant line is used, the present invention can obtain ON reflection characteristic better than that in the above case.
In the present invention, at least one distributed constant line opposing the projection of the movable element does not oppose a movable element main body serving as a portion of the movable element expect for the projection. That is, only the projection of the movable element opposes the distributed constant line. Accordingly, the width of the movable element opposing the distributed constant line is smaller than that of the distributed constant line as a whole. Thus, an OFF isolation characteristic similar to that in the case in which the movable element having the rectangular shape and the width smaller than that of the distributed constant line is used can be realized, and an ON reflection characteristic better than that in that case can be obtained.
In the present invention, at least one distributed constant line opposing the projection of the movable element also opposes a part of a movable element main body serving as a portion of said movable element expect for the projection. That is, the projection of the movable element and the part of the movable element main body oppose the distributed constant line. Thus, the opposing area between the movable element and the distributed constant line is increased as compared to the above invention, and, an OFF isolation characteristic can be improved as compared to the prior art.
In this case, the movable element main body of the movable element is formed to have a width equal to the width of the distributed constant line. Thus, there is almost no discontinuous portion between the distributed constant line and movable element, and an ON reflection characteristic better than that in the above invention can be obtained.
In the present invention, the projection of the movable element has a rectangular shape. When the rectangular projection is formed by notching two ends of the movable element, the opposing area between the movable element and the distributed constant line is a predetermined area even if the positioning error occurs in the longitudinal direction of the movable element.
In the present invention, the width of the projection of the movable element near the movable element main body serving as a portion of the movable element expect for the projection is made larger than that away from the movable element main body.
Since the width of the projection of the movable element near the movable element main body serving as a portion of the movable element expect for the projection

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