KR20020089787A - Rf mems switch - Google Patents

Abstract

PURPOSE: An RF MEMS(Micro Electro Mechanical System) switch is provided to reduce an insertion loss when an RF switch is turned on and improve a signal separation characteristic when the RF switch is turned off. CONSTITUTION: An input signal line(112) and two output signal lines(114) are formed on a dielectric substrate(100). An RF ground is formed on both sides of the input signal line(112) and the output signal lines(114). A gap(116) is formed between the input signal line(112) and the output signal lines(114). A contact plate(130) is formed to an upper direction of the gap(116). A driving electrode(140) is formed at both sides of the gap(116). A plurality of anchors(142) are formed on the driving electrode(140). A plurality of driving beams(144) are extended to an opposite direction of the anchors(142). An insulating portion(160) is inserted between the driving beams(144) and the contact plate(130). An insulating layer is formed on an RF ground(120) contacted with the driving beams(144). The RF grounds(120) are connected each other with a bridge(150). The bridge(150) is formed with a pillar(152) and a beam(154).

Description

RF MMS Switch {RF MEMS Switch}

The present invention relates to an RF MEMS switch, and more particularly, to an RF MEMS switch that insulates a contact plate connecting between signal lines to reduce loss of an RF signal.

The most widely used RF (Radio Frequency) device using MEMS (Micro Electro Mechanical System) technology is a switch. RF switches are widely used in signal routing and impedance matching networks in wireless communication terminals and systems in the microwave or millimeter wave band.

In conventional MMIC (Monolithic microwave integrated circuits) circuits, GaAs FETs or PIN diodes are mainly used to implement RF switches. However, when the switch is implemented using such a device, an insertion loss is large in the ON state and a signal separation characteristic in the OFF state is bad.

In order to remedy these shortcomings, researches on mechanical switches have been actively conducted, and in particular, MEMS switches are increasingly required due to the explosion of the mobile communication terminal market.

1 is a schematic cross-sectional view of a conventional RF switch. Referring to the drawings, a signal line 3 is formed on a substrate 10, an RF ground 4 is formed with the signal line 3 interposed therebetween, and an insulating film 5 is formed on the RF ground 4. A beam 6 extending from the anchors 2 and the anchors 2 is formed on both sides with the signal line 3 interposed therebetween. A contact plate 7 is formed below the beam 6 to contact the lower signal lines 3.

When the driving power is applied to the beam 6, the beam 6 bends down by the electrostatic force and the contact plate 7 contacts the signal line 3 so that the switch is turned on. However, in such a structure, in addition to the RF input signal going to the RF output signal, some signals flow through the beam 6 electrically connected to the contact plate 7, and thus, an additional part for blocking the signal must be added.

Accordingly, the present invention has been made to improve the above problems, and an object of the present invention is to provide an RF MEMS switch having a low insertion loss when the RF switch is in an ON state and good signal separation characteristics when the switch is in an OFF state.

Another object of the present invention is to provide a method of manufacturing the switch.

1 is a schematic cross-sectional view of a conventional RF switch,

2 is a perspective view of an RF MEMS switch according to a preferred embodiment of the present invention;

3 and 4 are cross-sectional views of portions cut along lines 3-3 'and 4-4' of FIG. 2, respectively;

5 is an electron micrograph of a preferred embodiment of the present invention,

6 to 8 are plan views and cross-sectional views showing various modifications of the connection form between the contact plate, the insulator and the driving beam of the present invention;

9A to 9I are cross-sectional views schematically showing a method of manufacturing the RF MEMS switch of the present invention.

Explanation of symbols on the main parts of the drawings

100: substrate 110: signal line

112: input signal line 114: output signal line

120: RF ground 122: insulating film

130: contact plate 140: driving electrode

142: anchor 144: drive beam

150: bridge 160: insulation

In order to achieve the above object, the RF MEMS switch of the present invention comprises a semiconductor or dielectric substrate; Signal lines formed on the substrate and having a gap forming an open circuit; RF grounds isolated from the signal line; Electrical wires connecting the RF grounds; Drive electrodes formed on the substrate; Anchors positioned on both sides of the gap on the driving electrode; Drive beams extending from an upper portion of the anchors; A contact plate positioned above the gap to form a resist structure with the signal lines; And an insulator extending from the driving beams to support the contact plate.

The electric wire includes: an anchor on the RF ground; And a beam connecting the anchor.

On the RF ground, it is preferable that further insulating films are formed to insulate between them when the upper driving beam falls.

The contact plate is divided into an upper part and a lower part through the insulating part, and a plurality of holes are formed in the insulating part for electrical connection between the upper part and the lower part, and the holes are preferably filled with metal.

It is preferable that the connection portions of the driving beams and the upper and lower portions of the contact plate are comb-shaped, and the insulating portion may be formed in a spring structure in which a plurality of long holes are formed.

It is preferable that a plurality of holes penetrating the contact plate and the insulating portion are formed.

According to another aspect of the present invention, there is provided a method of manufacturing an RF MEMS switch, comprising: (a) depositing a plating base layer on a substrate and then patterning a photoresist on the plating base layer to form an electroplating frame; (B) forming a signal line, an RF ground, and a driving electrode by electroplating on the plating base layer between the patterned electroplating molds; (C) removing the electroplating mold and removing the exposed plating base layer; (D) surface leveling by filling a photosensitive film between the signal line and the RF round; (E) forming a sacrificial layer with a photoresist on the planarized surface and forming a step for a contact plate on the gap between the input and output signals of the signal lines; (F) forming a contact plate on the stepped portion; (G) patterning an insulating part covering the contact plate; (H) forming a drive structure covering the drive electrode and a portion of the insulator; And (i) removing the sacrificial layer.

After the step (b), the step of patterning the insulating film on the part that can contact the driving electrode on the RF ground; further preferably.

Hereinafter, embodiments of the RF MEMS switch of the present invention will be described in detail with reference to the accompanying drawings.

Figure 2 is a perspective view of the RF MEMS switch according to a preferred embodiment of the present invention, Figures 3 and 4 are cross-sectional views of the cut portion along the line 3-3 'and 4-4' of FIG.

Referring to the drawings, one input signal line 112 and two output signal lines 114 are formed on the semiconductor or dielectric substrate 100, and RF ground 120 is formed on both sides of the signal lines 112 and 114. have. A gap 116 having a predetermined width is formed between the input signal line 112 and the output signal lines 114, and a contact plate is bent downward above the gap 116 to electrically connect the gap 116. 130 is formed. Driving electrodes 140 are formed at both sides with the gap 116 interposed therebetween, and anchors 142 are formed on the driving electrodes 140. Drive beams 144 extending in the opposite directions from the anchors 142 are formed, and the drive beams 144 and the contact plate 130 are provided with an insulating portion 160 to contact the contact plate 130. Is connected and supported. An insulating layer 122 is formed on the RF ground 120 in contact with the driving beam 144. The RF grounds 120 are formed with a bridge 150 for electrical connection to the pillars 152 formed thereon and the beams 154 therebetween.

The operation of the above embodiment will be described in detail with reference to the drawings.

First, when a pull-down DC voltage is applied to the anchor 142 and the driving beam 144 through the driving electrode 140, the driving beam is driven by an electrostatic force between the driving beam 144 and the RF ground 120. 144 is bent downward, so that the contact plate 130 passes through the gap 116 between the signal lines 110, thereby causing a resistance change between the contact plate 130 and the signal line 110. That is, when the contact plate 130 is in the normal position, the impedance is high, on the contrary, the contact plate 130 moves to the signal line 110 by the electrostatic force, and the impedance is lowered, and the switch is turned on.

The RF ground around the signal line provides the waveguide of the RF signal through the signal line with the signal line.

The insulation unit 160 prevents the RF signal from flowing to the ground 120 when the switch is turned on.

On the contrary, when the pull-down voltage is removed, the contact plate 130 is raised to the original position by the restoring force of the driving beam 144, and an air gap between the driving beam 144 and the RF ground 120 below the air is generated. gap) is formed so that the switch is in a high impedance state and is turned off.

The signal line 110 and the contact plate 130 of the structure form a resistive coupling, and an insulating layer 122 is formed at a contact portion between the driving beam 144 and the ground 120 to block electrical connection.

The bridge 150 between the RF grounds 120 is made directly on the hibernating surface instead of the conventional outward electrical connection, showing better RF signal characteristics.

5 is an electron micrograph of a preferred embodiment of the present invention. Referring to the drawings, it can be seen that the shape of the driving beam and the contact plate is slightly different from the simple shape of FIG. As such, the shape of the driving beam and the contact plate may be variously modified and will be described later.

6 to 8 show various modifications of the connection form between the contact plate, the insulator and the driving beam of the present invention.

First, referring to FIGS. 6A and 6B, the driving beams 144 are electrically separated from each other by an insulating part 160 provided at a lower portion thereof, and the contact plate 130 is connected to the upper part 132 and the lower part 134. The upper part 132 and the lower part 134 are electrically connected to each other by an electrical conductor filled in the plurality of holes 162 passing through the insulating part 160. In addition, a plurality of holes 164 penetrating through the contact plate 130 and the insulating portion 160 interposed therebetween is formed, which is used as a passage of the ash when removing the sacrificial layer to be described later in the manufacturing process. .

7A and 7B, the comb-shaped connecting portions 144a and 132a extending from the structure of FIG. 6 opposite the driving beam 144 and the upper portion of the contact plate 132 are formed on the insulating portion 160. It is a modified example. Accordingly, the deformation of the driving beam 144 due to the stress of the insulator is reduced.

8A through 8B illustrate another modified example of FIG. 6, in which a plurality of long holes 166 are formed in the insulating part 160 to serve as springs, and the upper parts 132 and the lower part 134 through the long holes 166. Since the upper and lower connection holes 162 in FIG. 6 are unnecessary.

In the above embodiment, a single pole double throw (SPDT) is shown, and a single input signal line and two output signal lines are shown. However, a single pole single throw (SPSP) and one input signal line are one. The output signal line may be extended and applied to more than one SPMT (Single Pole Multi Throw).

Table 1 shows RF characteristics measured by the HP8510 network analyzer, an RF measuring instrument, at a frequency of 2 GHz, using samples prepared by the modifications between the various contact plates and the insulation of FIGS. 6 to 8.

Unit: dB Sample Type Insertion loss Separation characteristics 6 0.138 42.1 7 0.134 42.1 8 0.677 43.2

In Table 1, both insertion loss and separation characteristics showed good characteristics at the frequency of 2 GHz.

Such a method of manufacturing the RF MEMS switch of the present invention is shown in schematic cross-sectional views in FIGS. 9A to 9I.

First, as shown in FIG. 9A, a plating base layer 102 of about 500 mW is deposited on the substrate 100, and then a photoresist is patterned on the plating base layer 102 to form an electroplating frame 104. Form.

Next, a signal line 110 having a thickness of 2 μm, an RF ground 120, and a driving electrode 140 are formed on the plating base layer 102 between the electroplating frames 104 by electroplating, and then electroplating. The mold 104 is removed, and thus the exposed plating base layer 102 is removed, and an insulating film 122 having a thickness of 0.1 μm is patterned on the RF ground 120 (see FIG. 9B).

Next, the surface is planarized by filling the photosensitive film 105 between the signal line 110 and the RF round 120 (see FIG. 9C).

A sacrificial layer 107 is then patterned on the planarized surface with a photoresist film (see FIG. 9D), and the gap between the input and output signals of the signal lines 110 (see reference numeral 116 in FIG. 2) is shown above. As shown in FIG. 9E, a step 109 for the bottom of the contact plate (see reference numeral 134 of FIG. 9F) is formed by dry etching using oxygen plasma to about 0.8 [mu] m.

Next, the lower surface 134 of the contact plate is formed by electroplating gold having a low surface resistance on the step 109.

Next, an insulating part 160 covering the contact plate lower part 134 is formed. In this case, a 0.3 μm thick silicon nitride film is formed and patterned by PECVD (Plasma Enhanced Chemical Vapor Deposition) method (see FIG. 9G).

After the driving structures 144 and 132 covering the driving electrode 140 and a part of the insulating part 160 are formed of gold, nickel plating, aluminum, or the like (see FIG. 9H), a sacrificial layer (reference number of FIG. 9H) 107) (see FIG. 9I).

As described above, the RF MEMS switch according to the present invention prevents the RF signal from flowing to the outside because the contact plate and the driving beam are connected to the insulator, and the insertion loss compared to the pin diode because it is on / off by metal contact. And signal separation characteristics are excellent.

Although the present invention has been described with reference to the embodiments with reference to the drawings, this is merely exemplary, it will be understood by those skilled in the art that various modifications and equivalent embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined only by the appended claims.

Claims (9)

Semiconductor or dielectric substrates; Signal lines formed on the substrate and having a gap forming an open circuit; RF grounds isolated from the signal line; Electrical wires connecting the RF grounds; Drive electrodes formed on the substrate; Anchors positioned on both sides of the gap on the driving electrode; Drive beams extending from an upper portion of the anchors; A contact plate positioned above the gap to form a resist structure with the signal lines; And And an insulating part extending from the driving beams so as to face the contact plate and supporting the contact plate. The method of claim 1, The electric wire includes: an anchor on the RF ground; And a beam connecting the anchors. The method of claim 1, The RF MEMS switch, characterized in that the insulating film is further formed on the RF ground to insulate between them when the upper driving beam is lowered. The method of claim 1, The contact plate is divided into an upper portion and a lower portion through the insulating portion, the plurality of holes are formed in the insulating portion for the electrical connection between the upper and lower, the holes are filled with a metal MEMS switch. The method of claim 4, wherein RF MEMS switch, characterized in that the connecting portion of the upper and lower portions of the drive beams and the contact plate. The method of claim 1, The insulation part is an RF MEMS switch, characterized in that the spring structure is formed with a plurality of holes. The method according to any one of claims 4 to 6, The RF MEMS switch, characterized in that a plurality of holes are formed through the contact plate and the insulating portion. (A) depositing a plating base layer on the substrate, patterning a photosensitive agent on the plating base layer to form an electroplating frame; (B) forming a signal line, an RF ground, and a driving electrode by electroplating on the plating base layer between the patterned electroplating molds; (C) removing the electroplating mold and removing the exposed plating base layer; (D) surface leveling by filling a photosensitive film between the signal line and the RF round; (E) forming a sacrificial layer with a photoresist on the planarized surface and forming a step for a contact plate on the gap between the input and output signals of the signal lines; (F) forming a contact plate on the stepped portion; (G) patterning an insulating part covering the contact plate; (H) forming a drive structure covering the drive electrode and a portion of the insulator; And (I) removing the sacrificial layer; RF MEMS switch manufacturing method comprising the. The method of claim 8, And (b) patterning an insulating film on a portion of the RF ground that can contact the driving electrode after the step (b).