Micromachine MEMS switch

[0002] The present invention relates to a micromachine switch used in a milliwave band to microwave band.

[0003] 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.

[0004] 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.

[0005] 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 102aand 102b. A GND plate 104 is disposed on the lower surface of the dielectric substrate 103.

[0006] The microstrip lines 102aand 102bare closely disposed apart from each other at a gap G. The switch electrode 113 is disposed between the microstrip lines 102aand 102bon the dielectric substrate 103. The switch electrode 113 is formed to have a height lower than that of each of the microstrip lines 102aand 102b.

[0007] 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.

[0008] 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 102aand 102b, respectively. The switch movable element 111 is formed to have a width equal to the width W of each of the microstrip lines 102aand 102b.

[0009] The switch movable element 111 is cantilevered on the support means 112 fixed on the dielectric substrate 103.

[0010] As shown in FIG. 13, the switch movable element 111 is generally arranged above the microstrip lines 102aand 102b. With this structure, since the switch movable element 111 is not in contact with the microstrip lines 102aand 102b, the micromachine switch 101 is in an OFF state. At this time, a little high-frequency energy is transmitted from the microstrip line 102ato the microstrip line 102b.

[0011] 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 102aand 102b, the switch movable element 111 is set in an ON state. At this time, the high-frequency energy from the microstrip line 102ais transmitted to the microstrip line 102bthrough the switch movable element 111.

[0012] As described above, the two ends of the switch movable element 111 oppose the microstrip lines 102aand 102b, respectively. Accordingly, the capacitor structures are also formed between the switch movable element 111 and the microstrip lines 102aand 102b.

[0013] This makes the capacitive coupling between the switch movable element 111 and microstrip lines 102aand 102bso that the high-frequency energy from the microstrip line 102aleaks out into the microstrip line 102beven if the micromachine switch 101 is in the OFF state. That is, in the conventional micromachine switch 101, an OFF isolation characteristic is poor.

[0014] In the microwave switching circuit, for example, the isolation of approximately 15 dB or more is required.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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 is made larger than that away from the movable element main body, the strength of the projection increases.

[0023] Also, 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 at least one distributed constant line includes a projection formed by notching at least one end of an edge of at least one distributed constant line on the movable element side, and a width of the projection is smaller than a length, serving as a width of the movable element, in a direction parallel to the widthwise direction of the distributed constant lines. That is, at least one end of the distributed constant line 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 movable element, and the projection is made to oppose the movable element. 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, a good ON reflection characteristic can be obtained 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.

[0024] In the present invention, the movable element does not oppose a distributed constant line main body serving as a portion, expect for the projection, of at least one distributed constant line having the projection. That is, only the projection of the distributed constant line opposes the movable element. Accordingly, 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.

[0025] In the present invention, the movable element also opposes a part of a distributed constant line main body serving as a portion, expect for the projection, of at least one distributed constant line having the projection. That is, the projection of the distributed constant line and the part of the distributed constant line main body oppose the movable element. Thus, an OFF isolation characteristic can be improved as compared to the above invention.

[0026] In this case, the movable element may be formed to have a width equal to the width of each of the distributed constant line main bodies. Thus, an ON reflection characteristic better than that in the above invention can be obtained.

[0027] In the present invention, the projection of at least one distributed constant line has a rectangular shape. Thus, even if the positioning error occurs in the longitudinal direction of the movable element, the opposing area between the movable element and the distributed constant line is a predetermined area.

[0028] In addition, 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 at least one distributed constant line includes a first projection formed by notching at least one end of an edge of at least one distributed constant line on the movable element side, and the movable element includes a second projection so formed as to oppose the first projection of at least one distributed constant line by notching at least one end of an edge of the movable element. With this structure, an OFF isolation characteristic of the micromachine switch can be improved. In addition, a good ON reflection characteristic can be obtained 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.

[0029] In the present invention, at least an entire lower surface of the movable element is made of a conductor.

[0030] In the present invention, the movable element is made of a conductive member and an insulating thin film formed on an entire lower surface of the conductive member.

[0031] In the present invention, the driving means comprises an electrode which is disposed apart between the distributed constant lines so as to oppose the movable element and to which a driving voltage is selectively applied.

[0032] In the present invention, the invention further comprises support means for supporting the movable element, the driving means is made of an upper electrode attached to the support means and a lower electrode disposed under the upper electrode and opposing the upper electrode, and a driving voltage is selectively applied to at least one of the upper and lower electrodes.

[0033] FIG. 1 is a perspective view showing the structure of a micromachine switch according to the first embodiment of the present invention;

[0034] FIG. 2 is a plan view of the micromachine switch shown in FIG. 1;

[0035] FIGS. 3A and 3B are sectional views taken along the line III-III′ of the micromachine switch shown in FIG. 2;

[0036] FIG. 4 is a plan view showing the main part of a micromachine switch according to the second embodiment of the present invention;

[0037] FIG. 5 is a plan view showing another shape of the switch movable element shown in FIG. 4;

[0038] FIG. 6 is a plan view showing still another shape of the switch movable element shown in FIG. 4;

[0039] FIG. 7 is a plan view showing the main part of micromachine switch according to the third embodiment of the present invention;

[0040] FIG. 8 is a plan view showing the main part of micromachine switch according to the fourth embodiment of the present invention;

[0041] FIG. 9 is a plan view showing the main part of a micromachine switch according to the fifth embodiment of the present invention;

[0042] FIG. 10 is a plan view showing the main part of a micromachine switch according to the sixth embodiment of the present invention;

[0043] FIG. 11 is a sectional view showing the section of a micromachine switch having another arrangement;

[0044] FIGS. 12A and 12B show sectional views of the sections of the switch movable elements;

[0045] FIG. 13 is a perspective view showing the structure of the conventional switch movable element; and

[0046] FIG. 14 is a plan view of the micromachine switch shown in FIG. 13.

[0047] A micromachine switch according to embodiments of the present invention will be described in detail below with reference to the accompanying drawings. A micromachine switch to be described here is a microswitch suitable for integration by a semiconductor element manufacturing process.

[0048] In a microstrip line (distributed constant line), the length of the microstrip line in a longitudinal direction is defined as a “length”, and the length of the microstrip line in a widthwise direction perpendicular to the longitudinal direction is defined as a “width”. In a movable element, the length in a direction parallel to the longitudinal direction of the microstrip line is defined as “length”, and the length in a direction parallel to the widthwise direction of the microstrip line is defined as a “width”.

[0049] FIG. 1 is a perspective view showing the structure of a micromachine switch according to the first embodiment of the present invention. FIG. 2 is a plan view of the micromachine switch shown in FIG. 1.

[0050] As shown in FIG. 1, a micromachine switch 1 is constructed by a switch movable element 11, support means 12, and switch electrode (driving means) 13. The micromachine switch 1 is formed on a dielectric substrate 3 together with two RF microstrip lines (distributed constant lines) 2aand 2b. A GND plate 4 is disposed on the lower surface of the dielectric substrate 3.

[0051] The microstrip lines 2aand 2bare closely disposed apart from each other at a gap G. The width of each of both microstrip lines 2aand 2bis W.

[0052] The switch electrode 13 is disposed apart between the microstrip lines 2aand 2bon the dielectric substrate 3. The switch electrode 13 is formed to have a height lower than that of each of the microstrip lines 2aand 2b. A driving voltage is selectively applied to the switch electrode 13 on the basis of an electrical signal.

[0053] The switch movable element 11 is arranged above the switch electrode 13. The switch movable element 11 is made of a conductive member. A capacitor structure is therefore formed by the switch electrode 13 and switch movable element 11 opposing each other.

[0054] On the other hand, the support means 12 for supporting the switch movable element 11 is constructed by a post portion 12aand arm portion 12b. The post portion 12ais fixed on the dielectric substrate 3 apart from the gap G between the microstrip lines 2aand 2bby a predetermined distance. The arm portion 12bextends from one end of the upper surface of the post portion 12ato the gap G. The support means 12 is made of a dielectric, semiconductor, or conductor.

[0055] The switch movable element 11 is fixed on a distal end of the arm portion 12bof the support means 12.

[0056] As shown in FIG. 2, the switch movable element 11 has a rectangular shape as a whole, and a length L of the switch movable element 11 is larger than the gap G. With this structure, distal end portions 11a′ and 11b′ of the switch movable element 11 oppose parts of distal end portions 2a′ and 2b′ of the microstrip lines 2aand 2b, respectively.

[0057] The distal end portions 11a′ and 11b′ of the switch movable element 11 are defined as portions each extending by a length (L−G)/2 from a corresponding one of the two ends of the switch movable element 11. The distal end portions 2a′ and 2b′ of the microstrip lines 2aand 2bare defined as portions each extending by a length (L−G)/2 from a corresponding one of opposing ends of the microstrip lines 2aand 2b.

[0058] Distal end portions 14a′ and 14b′, 15a′ and 15b′, and 16a′ and 16bof switch movable elements 14, 15, and 16, and microstrip lines 6aand 6band 7aand 7bof the distal end portions 6a′ and 6b′ and 7a′ and 7b′ (to be described later) have the same arrangement as described above.

[0059] A width a of the switch movable element 11 is smaller than the width W of each of the microstrip lines 2aand 2b. The area of each of the distal end portions 11a′ and 11b′ of the switch movable element 11 is therefore smaller than that of each of the distal end portions 2a′ and 2b′ of the microstrip lines 2aand 2b.

[0060] An operation of the micromachine switch 1 shown in FIG. 1 will be described next. FIGS. 3aand 3bare sectional view taken along the line III-III′ of the micromachine switch 1 shown in FIG. 2, in which FIG. 3(a) shows the OFF state of the micromachine switch 1, and FIG. 3(b) shows the ON state.

[0061] As shown in FIG. 3(a), the switch movable element 11 is generally positioned at a portion apart from the microstrip lines 2aand 2bby a height h. In this case, the height h is approximately several μm.

[0062] If, therefore, no driving voltage is applied to the switch electrode 13, the switch movable element 11 is not in contact with the microstrip lines 2aand 2b.

[0063] However, the switch movable element 11 has the portions opposing the microstrip lines 2aand 2b. Since the capacitor structure is. formed at these portions, the microstrip lines 2aand 2bare coupled to each other through the switch movable element 11.

[0064] A capacitance between the switch movable element 11 and the microstrip lines 2aand 2bis proportional to the opposing area between the switch movable element 11 and microstrip lines 2aand 2b. In the conventional micromachine switch 101 shown in FIG. 13, the width of the switch movable element 111 is equal to the width W of each of the microstrip lines 102aand 102b. Therefore, the opposing area between the switch movable element 111 and the microstrip lines 102aand 102bbecomes (L−G)×W.

[0065] In contrast to this, in the micromachine switch 1 shown in FIG. 1, the width a of the switch movable element 11 is smaller than the width W of each of the microstrip lines 2aand 2b. The width of the opposing portion between the switch movable element 11 and microstrip lines 2aand 2bis thus made small, and the opposite area becomes (L−G)×a.

[0066] In this manner, since the switch movable element 11 is formed to have the width a smaller than the width W of each of the microstrip lines 2aand 2b, thereby decreasing the opposing area and the capacitance formed between the switch movable element 11 and microstrip lines 2aand 2b. Since this weakens the coupling between the microstrip lines 2aand 2b, energy leakage can be suppressed in the OFF state of the micromachine switch 1.

[0067] The OFF isolation characteristics of the micromachine switch 1 according to the present invention shown in FIG. 1 and the conventional micromachine switch 101 shown in FIG. 13 will be described here.

[0068] Table 1 shows the calculation results of OFF isolation characteristics, which are obtained when predetermined parameters are set. More specifically, the thickness of each of the dielectric substrates 3 and 103 is H=200 μm; relative dielectric constant of each of the dielectric substrates 3 and 103, ∈r=4.6; the width, W=370 μm; the gap, G=200 μm; the height of each of the switch movable elements 11 and 111, h=5 μm; the length of each of the switch movable elements 11 and 111, L=260 μm; and a frequency of a high-frequency energy, 30 GHz. The width a of each of the switch movable elements 11 and 111 is shown in Table 1.

[0069] Assuming that letting Ein be an input energy from the microstrip line 2aor 102ato the switch movable element 11 or 111, and Eout be an output energy output from the switch movable element 11 or 111 to the microstrip line 2aor 102a. In this case, the isolation characteristic is obtained by equation {circle around (1)}.

[0070] (Isolation characteristic)=−10 log(Eout/Ein)  {circle around (1)}

[0071] As is obvious from equation {circle around (1)}, an increase in isolation characteristic value can implement a high degree of isolation. As shown in Table 1, a decrease in width a of each of the switch movable elements 11 and 25111 increases the isolation characteristic value. Therefore, an OFF isolation characteristic can be improved by using the micromachine switch 1 of the present invention as shown in FIG. 1.

[0072] The micromachine switch 1 shown in FIG. 1 is used for a microwave switching circuit, phase shifter, variable filter, or the like. For example, a microwave switching circuit requires an isolation of approximately 15 dB or more. If, therefore, the micromachine switch 1 shown in FIG. 1 is applied to the microwave switching circuit, the width a of the switch movable element 11 is set to 200 μm or less, thereby obtaining a good switching characteristic.

[0073] Note that, the required isolation changes depending on microwave or milliwave circuits to which the micromachine switch 1 is applied. Even if, therefore, the width a of the switch movable element 11 is 200 μm or more, the effect is obtained in some cases.

[0074] On the other hand, assume that a positive voltage is applied to the switch electrode 13 as a control voltage. In this case, positive charges appear on the surface of the switch electrode 13. Also, negative charges appear on the surface of the switch movable element 11 opposing the switch electrode 13 by electrostatic induction. An attraction force is generated by the electrostatic force between the positive charges of the switch electrode 13 and the negative charges of the switch movable element 11.

[0075] As shown in FIG. 3(b), this attraction force pulls down the switch movable element 11 toward the switch electrode 13. When the switch movable element 11 is brought into contact with the microstrip lines 2aand 2b, the micromachine switch 1 is turned on. At this time, the high-frequency energy is transmitted from the microstrip line 2ato the microstrip line 2bthrough the switch movable element 11.

[0076] FIG. 4 is a plan view showing the major part of a micromachine switch according to the second embodiment of the present invention. In FIG. 4, the same reference numerals as in FIG. 2 denote the same parts, and a detailed description thereof will be omitted. A switch movable element 14 shown in FIG. 4 is cantilevered on a support means 12, similar to the switch movable element 11 shown in FIG. 2. A switch electrode 13 is disposed at a gap G between microstrip lines 2aand 2b. In FIG. 4, however, the description of the support means 12 and switch electrode 13 is omitted.

[0077] This also applies to FIGS. 5 to 9 (to be described later).

[0078] A micromachine switch 1 shown in FIG. 4 uses the switch movable element 14 shown in FIG. 4 in place of the switch movable element 11 shown in FIG. 1.

[0079] The two ends of an edge of the switch movable element 14 on the microstrip line 2aside are notched to form a projection (second projection) 52a. Similarly, the two ends of the edge of the switch movable element 14 on the microstrip line 2bside are notched to form a projection (second projection) 52b.

[0080] In this case, a portion of the switch movable element 14 except the projections 52aand 52bis defined as a movable element main body 51. More specifically, the movable element main body 51 is a portion of the switch movable element 14 having a width b. Similarly, a portion of a switch movable element 15 except for projections 54aand 54bis defined as a movable element main body 53. More specifically, the movable element main body 53 is a portion of the switch movable element 15 having a width b.

[0081] Each of the projections 52aand 52bhas a rectangular shape. A width a of each of the projections 52aand 52bis smaller than the width W of each of the microstrip lines 2aand 2b.

[0082] Since a length c of the movable element main body 51 is a smaller than the gap G between the microstrip lines 2aand 2b, the movable element main body 51 is not included in distal end portions 14a′ and 14b′ of the switch movable element 14. That is, the movable element main body 51 does not oppose the microstrip lines 2aand 2b.

[0083] Similar to the micromachine switch 1 shown in FIG. 1, the opposing area between the switch movable element 14 and the microstrip lines 2aand 2bthus becomes (L−G)×a. That is, the isolation characteristic equal to that obtained by the micromachine switch 1 shown in FIG. 1 can be obtained by the micromachine switch 1 shown in FIG. 4.

[0084] Since the impedance of a line is related to the surface area of the line, a decrease in width of the line increases the impedance. For this reason, if the width of the whole switch movable element 11 decreases, like the micromachine switch 1 shown in FIG. 1, the characteristic impedance on the gap G increases in the ON state of the micromachine switch 1.

[0085] 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, the reflection increases in the ON state of the micromachine switch 1.

[0086] In contrast to this, in the switch movable element 14 shown in FIG. 4, the width b of the movable element main body 51 is larger than the width a of each of the projections 52aand 52brespectively opposing the microstrip lines 2aand 2b. More specifically, the width b of the movable element main body 51 is closer to the width W of each of the microstrip lines 2aand 2bthan the width a of each of the projections 52aand 52b. Accordingly, the impedance mismatching in the switch movable element 14 is reduced, thereby suppressing the reflection of the high-frequency energy in the ON state.

[0087] The OFF isolation characteristics and ON reflection characteristics of the micromachine switches 1 shown in FIGS. 1 and 4 will be described.

[0088] Table 2 shows the calculation results of OFF isolation characteristics and ON reflection characteristics, which are obtained when predetermined parameters are set. Parameters except for a, b, and c are the same as those shown in Table 1.

[0089] Letting Ein be the input energy input from the microstrip line 2aor 102ato the switch movable element 11 or 14, and Ere be the reflection energy from switch movable element 11 or 14 to the microstrip line 2aor 102a, the reflection characteristic is obtained by equation {circle around (2)}.

[0090] (Reflection characteristic)=10 log(Ere/Ein)  {circle around (2)}

[0091] As is obvious in equation {circle around (2)}, a decrease in reflection characteristic value reduces the energy loss.

[0092] In Table 2, the switch movable element 14 is compared with the switch movable element 11 when a=100 μm. The isolation characteristic values of the elements 14 and 11 are equal as 18 dB. However, the value of the reflection characteristic of the switch movable element 14 is smaller than that of the switch movable element 11. In this manner, the energy loss can be improved in the ON state by using the switch movable element 14 shown in FIG. 4.

[0093] Note that, the sizes L, a, b, and c of the switch movable element 14 are set based on the sizes W and G of the microstrip lines 2aand 2b, thereby selecting appropriate isolation and reflection characteristics.

[0094] FIGS. 5 and 6 are plan views each showing another shape of the switch movable element 14 shown in FIG. 4.

[0095] As shown in FIG. 5, the switch movable element 14 may be obtained by notching one end of an edge of the switch movable element 14 on each of the microstrip lines 2aand 2b. In the switch movable element 14 shown in FIG. 5, the opposing area between the switch movable element 14 and the microstrip lines 2aand 2bincreases as compared to that of the switch movable element 14 shown in FIG. 4. However, an OFF isolation characteristic better than that of the conventional micromachine switch 1 shown in FIG. 13 can be obtained.

[0096] In addition, the shape of each of the projections 52aand 52bof the switch movable element 14 is not limited to the rectangular shape. For example, as shown in FIG. 6, each of the projections (second projections) 52aand 52bmay have a trapezoidal shape. The width of each of the projections 51aand 52bnear the movable element main body 51 is made larger than that away from the movable element main body 51. This can increase the strength of the switch movable element 14.

[0097] Note that, the width b of the movable element main body 51 of the switch movable element 14 shown in FIGS. 4 to 6 is smaller than the W of each of the microstrip lines 2aand 2b. However, the width b of the movable element main body 51 may be made large within the range in which no reflection characteristic greatly degrades.

[0098] FIG. 7 is a plan view showing the main part of a micromachine switch according to the third embodiment of the present invention. A switch movable element 15 shown in FIG. 7 is different from the switch movable element 14 in FIG. 4 in that a length c of a movable element main body 53 is larger than a gap G, and a width b of the movable element main body 53 is equal to a width W of each of microstrip lines 2aand 2b. In FIG. 7, reference numerals 54aand 54bdenote projections (second projections).

[0099] Since the length c of the movable element main body 53 is larger than the gap G, the portions of the movable element main body 53 are included in distal end portions 15a′ and 15b′ of the switch movable element 15. That is, the portions of the movable element main body 53 oppose the microstrip lines 2aand 2b, respectively.

[0100] Thus, the opposing area between the switch movable element 15 in FIG. 7 and microstrip lines 2aand 2bbecomes larger than that shown in FIG. 4. By using the switch movable element 15 in FIG. 7, therefore, an OFF isolation characteristic becomes worse than that by using the switch movable element 11 or 14 in FIG. 1 or 4. Even if so, the isolation characteristic better than that in the prior art can be obtained.

[0101] Since, however, the length c of the movable element main body 53 is larger than the gap G, the notched portions of the switch movable element 15 are not present on the gap G. In addition, the width b of the movable element main body 53 is equal to the width W of each of the microstrip lines 2aand 2b.

[0102] With this arrangement, the discontinuous portion of the micromachine switch 1 in the ON state shown in FIG. 7 is only a portion where the switch movable element 15 is in contact with the microstrip lines 2aand 2b. By using the switch movable element 15 in FIG. 7, therefore, an ON reflection characteristic can be improved better than that in the switch movable element shown in FIG. 4.

[0103] The width b of the movable element main body 53 is equal to the width W of each of the microstrip lines 2aand 2b. The effect can be obtained even if the width b is completely equal to the width W.

[0104] The switch movable element 15 may be obtained by notching one end of an edge of the switch movable element 15 on each of the microstrip lines 2aand 2b.

[0105] In addition, each of projections 54aand 54bof the switch movable element 15 is not limited to have the rectangular shape and, for example, may have a trapezoidal shape.

[0106] FIG. 8 is a plan view showing the main part of a micromachine switch according to the fourth embodiment of the present invention.

[0107] As shown in FIG. 8, a switch movable element 16 has a rectangular shape. On the other hand, in a microstrip line 6a, the two ends of an edge of the microstrip line 6aon the switch movable element 16 side are notched to form a projection (first projection) 62a. Similarly, in a microstrip line 6b, the two ends of the edge of the microstrip line 6bon the switch movable element 16 side are notched to form a projection (first projection) 62b.

[0108] In this case, portions of the microstrip lines 6aand 6bexcept for the projections 62aand 62bare defined as line main bodies 61aand 62b, respectively. More specifically, the line main bodies 61aand 61bare portions of the microstrip lines 6aand 6beach having a width W. Similarly, portions of microstrip lines 7aand 7bexcept for projections 72aand 72bare defined as line main bodies 71aand 71b, respectively. More specifically, the line main bodies 71aand 71bare portions of the microstrip lines 7aand 7beach having the width W.

[0109] Each of the projections 62aand 62bhas a rectangular shape. A width d of each of the projections 62aand 62bis smaller than a width e of the switch movable element 16.

[0110] A distance D between the line main bodies 61aand 61bof the microstrip lines 6aand 6bis larger than a length L of the switch movable element 16. With this structure, the line main bodies 61aand 61bare not included in distal end portions 6a′ and 6b′ of the microstrip lines 6aand 6b, respectively. That is, the line main bodies 61aand 61bdo not oppose the switch movable element 16.

[0111] In this manner, in a micromachine switch 1 shown in FIG. 8, the projections 62aand 62bare formed in the microstrip lines 6aand 6b, respectively, in place of forming the projections 52aand 52bin the switch movable element 14 in the micromachine switch 1 shown in FIG. 4. Other parts in this embodiment are the same as those in the micromachine switch 1 shown in FIG. 4.

[0112] Therefore, for example, each of the projections 62aand 62bof the microstrip lines 6aand 6bcan be formed by notching one end of an edge of a corresponding one of the microstrip lines 6aand 6bon the switch movable element 16 side. In addition, each of projections 54aand 54bis not limited to have the rectangular shape and, for example, may have a trapezoidal shape.

[0113] Even if the micromachine switch 1 is formed in such a manner, the effect similar to that of the micromachine switch 1 shown in FIG. 4 can be obtained.

[0114] FIG. 9 is a plan view showing the main part of a micromachine switch according to the fifth embodiment of the present invention. The micromachine switch shown in FIG. 9 is different from the micromachine switch 1 shown in FIG. 8 in the following points.

[0115] First, a distance D between line main bodies 71aand 71bof microstrip lines 7aand 7bis smaller than a length L of a switch movable element 16. With this structure, the line main bodies 71aand 71bare included in distal end portions 7a′ and 7b′ of the microstrip lines 7aand 7b, respectively. That is, the line main bodies 71aand 71boppose the switch movable element 16.

[0116] In addition, a width e of the switch movable element 16 is equal to a width W of each of the microstrip lines 7aand 7b. Other parts in this embodiment are the same as those in the micromachine switch 1 shown in FIG. 8. In FIG. 9, reference numerals 72aand 72bdenote projections (first projections).

[0117] Even if a micromachine switch 1 is disposed in such a manner, the effect similar to that of the micromachine switch 1 shown in FIG. 7 can be obtained.

[0118] Note that, the width e of the switch movable element 16 is equal to the width W of each of the microstrip lines 7aand 7b. The effect can be obtained even if the width e is not completely equal to the width W.

[0119] FIG. 10 is a plan view showing the main part of a micromachine switch according to the sixth embodiment of the present invention. The micromachine switch shown in FIG. 10 is formed by combining the switch movable element 14 shown in FIG. 4 with the microstrip lines 6aand 6bshown in FIG. 8.

[0120] In this manner, even if both switch movable element 14 and microstrip lines 6aand 6bare notched, the opposing area between the switch movable element 14 and microstrip lines 6aand 6bcan be decreased, thereby improving the OFF isolation characteristic of a micromachine switch 1.

[0121] Note that, a width a of each of the projections 52aand 52bof the switch movable element 14 may be equal to or different from a width d of each of projections 62aand 62bof the microstrip lines 6aand 6b.

[0122] In addition, each of the switch movable elements 14 and 15 shown in FIGS. 5 to 7 may be used in place of the switch movable element 14 shown in FIG. 4, and the microstrip lines 7aand 7bshown in FIG. 9 may be used in place of the microstrip lines 6aand 6bshown in FIG. 8.

[0123] As described above, the embodiments of the present invention have been described by using the micromachine switch 1 having the arrangement in which a switch electrode 13 is disposed on a gap G. The present invention is, however, applied to a micromachine switch 8 having the sectional shape shown in FIG. 11.

[0124] That is, the micromachine switch 8 shown in FIG. 11 has an upper electrode 13aand lower electrode 13bas switch electrodes (driving means). The lower electrode 13bis formed on a dielectric substrate 3, below an arm portion 12bof a support means, and is not sandwiched between microstrip lines 2aand 2b(or 6aand 6bor 7aand 7b). The upper electrode 13ais tightly formed on the upper surface of the arm portion 12b. The upper and lower electrodes 13aand 13bsandwich the arm portion 12btherebetween and oppose each other. The arm portion 12bis made of an insulating member.

[0125] A driving voltage is selectively applied to at least one of the upper and lower electrodes 13aand 13b. The arm portion 12bis pulled down by an electrostatic force, and a switch movable element 11 (or 14, 15, or 16) is brought into contact with the microstrip lines 2aand 2b(or 6aand 6bor 7aand 7b).

[0126] Even if the present invention is applied to this micromachine switch 8, the effect described above can be obtained.

[0127] In any one of the switch movable elements 14 and 15 in the FIGS. 4 to 7, the two sides of the switch movable element 14 or 15 are notched to form projections 52aand 52bor 54aand 54b. However, even if the projection 52aor 52bis formed on only one side of the switch movable element 14, or even if the projection 54aor 54bis formed on only one side of the switch movable element 15, the effect can be obtained.

[0128] This also applies to the microstrip lines 6aand 6band 7aand 7bin FIGS. 8 and 9. More specifically, even if the projection 62aor 62bis formed in only one of the microstrip lines 6aand 6b, or even if the projection 72aor 72bis formed in only one of the microstrip lines 7aand 7b, the effect can be obtained.

[0129] In addition, each of the micromachine switches 1 and 8 shown in FIGS. 1 to 11 connects/disconnects two microstrip lines 2aand 2b(or 6aand 6bor 7aand 7b) to/from each other. However, the present invention is also applied to each of the micromachine switch 1 and 8 connecting/disconnecting three or more microstrip lines to/from each other.

[0130] In describing the embodiments of the present invention, the microstrip lines 2aand 2b(or 6aand 6bor 7aand 7b) are used as distributed constant lines. Even if, however, coplanar lines, triplet lines, or slot lines are used as the distributed constant lines, the same effect can be obtained.

[0131] The micromachine switch 1 or 8 shown in FIGS. 1 to 11 may be an ohmic connection type micromachine switch or capacitive connection type micromachine switch.

[0132] In an ohmic connection type micromachine switch 1 or 8, the whole switch movable elements 11 and 14 to 16 may be made of conductive members. As shown in FIG. 12(a), each of the switch movable elements 11 and 14 to 16 may be constructed by a member 81 of a semiconductor or insulator, and a conductive film 82 formed on the entire lower surface of the member 81 (i.e., the surface opposite to the microstrip lines 2aand 2bor the like). That is, in the switch movable elements 11 and 14 to 16, at least the entire lower surface of each of the switch movable elements 11 and 14 to 16 may be made of a conductor.

[0133] In addition, as shown in FIG. 12(b), a capacitive connection type micromachine switch 1 or 8 is constructed by a conductive member 83 and insulating thin film 84 formed on the lower surface of the conductive member 83 (i.e., the surface opposing the microstrip lines 2aand 2bor the like).

[0134] A micromachine switch according to the present invention is suitable for a switch device for high-frequency circuits such as a phase shifter and frequency variable filter used in a milliwave band to microwave band.