Terahertz-band high-capacitance-ratio metal parallel RF MEMS switch

Abstract

The invention discloses a metal parallel RF MEMS switch with a high capacitance ratio in a terahertz wave band, and belongs to the field of radio frequency front-end devices. The overall structure is composed of a branch port metal block, a direct current bias line, a microstrip line matching structure, a metal beam MEMS switch, a metal electrode of a metal beam, a silicon nitride insulating layer, a silicon-based substrate, a coplanar waveguide metal ground and a metal ground. A metal anchor point of the metal beam is connected to the coplanar waveguide metal ground, a direct current port on the right upper side is connected to the coplanar waveguide metal ground through a direct current bias line, and a direct current port on the left upper side is connected to the metal electrode through a direct current bias line. Different direct-current voltages can be input into the direct-current port on the left side to control the state of the metal beam lifting up and the state of being adsorbed to the electrode, and the states correspond to the on-off state of the switch. The parallel MEMS switch designed by the invention works between 103.33 G and 170G, and ensures that the isolation degree in an off state is higher than 33.67 dB; and the insertion loss in a conducting state is lower than 0.8 dB. The reaction time of microsecond magnitude is achieved, and destructive deformation is not prone to occurring; the structure is simple.

Description

Technical Field

[0001] The present invention relates to a design of a high capacitance ratio metal parallel RF MEMS switch, which is mainly used in satellite communication systems in the terahertz frequency band and belongs to the field of radio frequency front-end devices. Background Art

[0002] The essence of RF MEMS switches is to efficiently and accurately control the on-off status of circuits. Compared with traditional PIN diode switches or varactor diode switches, RF MEMS switches have the advantages of small size, light weight, insensitivity to acceleration, no DC loss at microwave frequencies, high isolation, low power consumption and low insertion loss. For terahertz band communication systems, traditional PIN diode switches or varactor diode switches have problems such as excessively high loss characteristics, low isolation, and low linear characteristics in the high frequency band, and are not suitable for use in high frequency band communication systems. Therefore, RF MEMS switches are widely used in phased array antennas, switch matrices of satellite switching networks, reconfigurable antennas, radars, and drones in the high frequency band.

[0003] According to the existing theoretical knowledge of MEMS switches, MEMS switches can be divided into active MEMS switches and passive MEMS switches according to the requirements of external power supply. Active MEMS switches include electrical, mechanical, photochemical and similar energy fields converted into mechanical energy to generate displacement, and have good driving performance; passive MEMS switches use their own structure to collect energy for inertial actuators, and have excellent storage efficiency and anti-electromagnetic wave interference capabilities; according to different contact modes, MEMS switches can be divided into capacitive MEMS and resistive MEMS. Capacitive MEMS switches are suitable for high-frequency applications above 30MHZ, and use capacitive coupling to achieve the on and off states of the circuit; resistive MEMS switches are suitable for low-frequency applications of 30kHZ-300kHz; MEMS switches can also be divided into silicon-based switches and non-silicon-based switches according to different processing materials. Silicon-based switches have high resistance and will produce large insertion losses during application, while non-silicon-based switches are mainly metal switches. Metal switches can solve the problem of large contact resistance, but the microstructure manufacturing of metals is not yet mature. During the manufacturing process, the switch may be deformed, so the product yield is low. In the published works, there are few MEMS switches with high isolation, low insertion loss and low power consumption applied in the terahertz high frequency band. For example, in 2016, Theodore Reck et al. proposed a RF MEMS waveguide reflection switch working at 700GHZ, and achieved an isolation of more than 20dB and an insertion loss of 3dB in the entire frequency band, with a high insertion loss; in 2017, Feng Yukang and Scott Barker proposed a RF MEMS DC contact switch working at 500-750GHZ, which achieved an isolation of 17-22dB and an insertion loss of 1.3-2.65dB, with a high insertion loss, and the switch was made on high-resistance silicon as a waveguide switch, which is not easy to integrate.

[0004] In summary, there are currently very few MEMS switches that work in the terahertz band, and most of them do not have good insertion loss characteristics and cannot meet the requirements for communication equipment applications in the terahertz band. Summary of the invention

[0005] In order to solve the problems existing in the background technology, the present invention proposes a metal parallel RF MEMS switch with high capacitance ratio in the terahertz band. The RF MEMS switch uses a floating metal film in the middle of the conductive structure to increase the capacitance of the switch, and has the characteristics of simple structure, high isolation, low insertion loss, low power consumption, and not easy to produce structural deformation, and can be used in the terahertz band.

[0006] In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

[0007] A metal parallel RF MEMS switch with a high capacitance ratio in the terahertz band, comprising a coplanar waveguide metal ground 14, a silicon-based substrate 15 and a metal ground 42, wherein the coplanar waveguide metal ground 14 is located on the upper surface of the silicon-based substrate 15; the metal ground 42 is located on the lower surface of the silicon-based substrate 15; and further comprising a DC port metal block, a DC bias line, a microstrip line matching structure 13 and a metal beam MEMS switch; the metal electrodes of the DC port metal block, the microstrip line matching structure 13 and the metal beam MEMS switch are all located on the upper surface of the silicon-based substrate 15;

[0008] The microstrip line matching structure 13 is located in the area surrounded by the coplanar waveguide metal ground, and a silicon nitride film is arranged in the middle position;

[0009] The bridge piers on both sides of the metal beam MEMS switch are located on the coplanar waveguide metal ground and are placed directly above the silicon nitride film; there are two groups of DC port metal blocks, both groups of DC port metal blocks are located outside the area surrounded by the coplanar waveguide metal ground, one group of DC port metal blocks is connected to the coplanar waveguide metal ground, and the other DC port metal block is connected to the metal electrode of the metal beam MEMS switch.

[0010] Furthermore, the metal beam MEMS switch includes a left bridge pier, a left folding arm, a left action arm, a left middle arm, an H-shaped structure, a right middle arm, a right action arm, a right folding arm and a right bridge pier, which are connected in sequence from left to right; wherein the left action arm, the left middle arm, the right action arm and the middle arm are all corroded with periodic circular holes; and the intermediate conduction structure of the H-shaped structure micro metal beam MEMS switch.

[0011] Furthermore, the middle conduction structure of the metal beam MEMS switch is an H-type structure, and there are two cylindrical contacts on both sides of the lower surface of the H-type structure. The H-type structure is suspended directly above the silicon nitride film. When the metal beam MEMS switch is closed, the cylindrical contacts are in contact with the upper surface of the silicon nitride film.

[0012] Furthermore, the microstrip line matching structure 13 is symmetrical about its center, and is composed of input and output microstrip lines and an intermediate trapezoidal gradient matching structure connected to the inner ends thereof, for matching; the intermediate conduction structure 18 of the metal beam MEMS switch 11 is located directly above the intermediate trapezoidal gradient matching structure, and when the intermediate conduction structure of the metal beam MEMS switch 11 is suspended in the air, conduction is achieved.

[0013] Furthermore, a silicon nitride insulating layer is provided on the upper surface of the metal electrode of the metal beam MEMS switch 11, and the two metal electrodes correspond to the left action arm and the right action arm respectively. The metal electrodes are located directly below the corresponding action arms to pull down the action arms when power is turned on.

[0014] Compared with the background technology, the present invention has the following advantages:

[0015] a) The structure is simple and easy to manufacture. It can be applied to radio frequency circuits such as phased array antennas and metasurface reflective array antennas to control their conduction and disconnection.

[0016] b) An H-shaped floating metal film is provided under the H-shaped metal sheet in the middle of the metal beam to effectively block the flow of signals.

[0017] c) High isolation in the switch-off state and low insertion loss in the switch-on state.

[0018] d) The switch adopts a folding structure, which greatly reduces the driving voltage of the switch. It can work when the driving voltage is 15V, with short response time and high reliability. The switch is not easy to break during operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a top view of the overall structure of the present invention;

[0020] Figure 2 It is a schematic diagram of the structure of the present invention when the overall structure is not conducting;

[0021] Figure 3 It is a schematic diagram of the structure of the overall structure of the present invention;

[0022] Figure 4 It is a structural schematic diagram of the metal beam MEMS switch in the present invention;

[0023] Figure 5 It is a bottom view of the structure of the middle conductive structure of the metal beam MEMS switch in the present invention;

[0024] Figure 6 It is a three-dimensional stereogram of the overall structure of the present invention;

[0025] Figure 7 is the isolation S of the metal parallel MEMS switch in the disconnected state of the present invention 21 curve;

[0026] Figure 8 is the insertion loss S of the metal parallel MEMS switch in the on state of the present invention 21 curve;

[0027] Fig. 9 is the return loss S of the metal parallel MEMS switch in the disconnected state of the present invention 11 curve;

[0028] Fig.10 is the return loss S of the metal parallel MEMS switch in the on state of the present invention 11 curve; DETAILED DESCRIPTION

[0029] The following is combined with Figure 1-8The specific implementation modes of the present invention are further described in detail with reference to the accompanying drawings and examples.

[0030] A metal parallel RF MEMS switch with a high capacitance ratio in the terahertz band comprises a silicon-based substrate, a metal ground, a DC port metal block, a DC bias line, a microstrip line matching structure, and a metal beam MEMS switch; the coplanar waveguide metal ground is located on the upper surface of the silicon-based substrate; the metal ground is located on the lower surface of the silicon-based substrate; the DC port metal block, the metal electrode of the metal beam, and the microstrip line matching structure are all located on the upper surface of the silicon-based substrate;

[0031] There are two DC port metal blocks in total, which are divided into two groups. Both groups of DC port metal blocks are located on the left side of the microstrip line matching structure. Metal beam MEMS switches are arranged between the two groups of DC port metal blocks and the microstrip line matching structure. Both metal beam MEMS switches are located above the microstrip line matching structure.

[0032] The intermediate conduction structure of the metal beam MEMS switch is an H-shaped metal sheet, under which there is an H-shaped floating metal film, and under which there are four cylindrical contacts.

[0033] The metal beam MEMS switch includes a left bridge pier, a left folding arm, a left action arm, a left middle arm, an H-shaped structure, a right middle arm, a right action arm, a right folding arm and a right bridge pier, which are connected from left to right in sequence; wherein the left action arm, the left middle arm, the right action arm and the middle arm are all corroded with periodic circular holes.

[0034] The left rectangular ring and the right rectangular ring of the metal beam MEMS switch have the same structure and are equal in size; the left rectangular ring and the right rectangular ring are respectively opposite to the outer rectangular ring on the same side in upper and lower positions; the left folding arm and the right folding arm have the same structure and are equal in size; the left action arm and the right action arm have the same structure and are equal in size, and the left middle arm and the right middle arm have the same structure and are equal in size.

[0035] The microstrip line matching structure is composed of an input and output microstrip line and an intermediate trapezoidal gradient matching structure connected to the inner end thereof, and is used for matching. The intermediate conduction structure of the metal beam MEMS switch is located directly above the intermediate trapezoidal gradient matching structure. When the intermediate conduction structure of the metal beam MEMS switch is stationary, conduction is achieved.

[0036] A silicon nitride insulating layer is provided on the upper surface of the metal electrode of the metal beam MEMS switch and on the microstrip line directly below the middle conductive structure of the metal beam MEMS switch.

[0037] Attach Figure 1 and attached Figure 6Taking a metal parallel RF MEMS switch with high capacitance ratio in the terahertz band as an example, this embodiment includes DC port metal blocks 1, 2, DC bias lines 3, 4, 5, microstrip line matching structures 1, 3, metal beam MEMS switch bridge piers 11, 12, metal beam intermediate conductive structure 18, metal electrodes 20, 22 of the metal beam, silicon nitride insulating layers 17, 19 on the upper surface of the metal electrodes of the metal beam, silicon-based substrate 15, coplanar waveguide metal ground 14, metal ground 42; since the performance of ordinary metal beam MEMS switches is poor, it will cause low isolation, so a floating metal film is added under the transmission line to improve the isolation of the switch, and the metal beam is directly composed of a fixed beam composed of a structure symmetrical with an H-shaped structure. The metal beam and the metal electrodes 20, 22 distributed on both sides of the metal beam are connected to the DC port metal block 1 on the same side through DC bias lines 3, 4 respectively.

[0038] The material of the silicon-based substrate 15 is silicon-based with a dielectric constant of 3.78 and a thickness of 100 um.

[0039] The overall structure is in a disconnected state as shown in the attached Figure 3 , the DC port metal block 2 is grounded or at the same voltage, and the metal beam switch gives the metal beam and the metal electrode grounding and driving voltage through the DC port metal block 1. The driving voltage generates an electrostatic force between the metal electrode and the metal beam, causing the metal beam 12 to produce a longitudinal deformation, pulling the metal beam down as a whole, and finally making the contact below the middle conductive structure 15 of the metal beam switch contact with the top of the microstrip line matching structure 13, so that the overall structure is in a disconnected state; if the switch is to be in a conductive state, as shown in the attached Figure 2 The DC port metal block 2 is grounded or at the same voltage, and the DC port metal block 1 is not connected to voltage. At this time, the metal beam switch 12 does not deform, and the middle conductive structure 15 of the metal beam switch is located directly above the microstrip line 13. The two do not contact each other. At this time, the signal is directly transmitted from the microstrip line to the other port, and finally the overall structure is in a conductive state.

[0040] As attached Figure 4 As shown, the metal beam is a symmetrical structure, which is composed of rectangular structures of different sizes, including a rectangular ring 28, folding arms (30, 31, 32, 33), a connecting arm 35, an action arm 37, and an H-shaped structure 40. The connecting arm 35 and the action arm 37 are etched with periodic cylindrical holes, and the size of the action arm 37 is exactly the same as that of the connecting arm 35.

[0041] The above-mentioned design of the metal parallel form based on the floating metal film is to increase the isolation size of the switch, reduce the insertion loss, and improve the overall performance of the switch; the metal beam is designed as a folded structure to reduce the pull-down driving voltage, shorten the response time, reduce the residual stress, and achieve high-speed and reliable performance of the switch. In this example, the driving voltage can be controlled at 10-15V.

[0042] As attached Figure 5 As shown, the conductive structure in the middle of the metal beam is an H-shaped metal sheet, and two cylindrical contacts are distributed on both sides of the center position below the Y-shaped metal sheet. The purpose of the structural design is to increase the isolation of the switch and reduce the insertion loss and power consumption of the switch.

[0043] Attached Figures 7 to 10 Insertion loss S11 and isolation S21 performance scattering parameter curves when the switch is in the off and on states respectively.

[0044] The size parameters of the intermediate conduction structure and the microstrip line matching structure will affect the RF performance of the switch. The size of the metal beam and metal electrode will affect the performance of the driving voltage, which is mainly manifested as follows:

[0045] A. The narrower the overall width of the intermediate conduction structure, the better the isolation of the switch in the off state. The switch of this design adopts a metal parallel form, with an H-shaped floating metal film under the intermediate conduction structure. The isolation can be optimized by adjusting the size of the conduction structure and the size of the floating metal film.

[0046] B. The longer the overall length of the switch and the longer the disconnection length of the microstrip line matching structure, the better the switch isolation and the lower the driving voltage will be. However, it will increase the possibility of destructive deformation of the switch, resulting in reduced switch reliability. It will also increase the overall structural size of the switch, affecting layout and use.

[0047] C. The size of the microstrip line matching structure will affect the switching loss characteristics when the switch is in the on state. This design adopts a gradual structure from the microstrip line width to the conduction structure width, which is beneficial to reduce the insertion loss when the switch is in the on state.

[0048] D. The size of the metal beam switch mainly affects the performance of the driving voltage and response time. This design adopts a folding structure and continuously optimizes the sizes of the rectangular ring, connecting arm, action arm and H-type structure to stabilize the working voltage of the driving voltage between 10-15V and the response time at the order of microseconds.

[0049] E. The size and spacing of the periodic cylindrical holes will affect the magnitude of the electrostatic force between the metal electrode and the beam, and thus will also affect the working voltage of the driving voltage.

[0050] Therefore, choosing the appropriate metal beam size, metal beam conduction structure size and microstrip line matching structure size is crucial to improving the overall switch performance.

[0051] The following selects a size combination to introduce the size of the structure in the attached figure. The following data is in micrometers;

[0052] Figure 2 The dimensions of the structure are:

[0053] The length of structure 16 is 10; the side length of the silicon nitride insulating layers 17 and 19 of the electrodes is 40; the length of structures 20 and 22 is 40; the thickness of structure 27 is 0.2; the diameter of the cylindrical contact below the conductive structure 18 in the middle of the metal beam = 3; the thickness of the silicon nitride insulating layer = 0.1;

[0054] As attached Figure 4 The dimensions of the structure are:

[0055] The length of structure 28 is 60; the length of structure 29 is 10; the length of structure 30 is 20; the length of structure 31 is 30; the length of structure 32 is 20; the length of structure 33 is 35; the length of structure 34 is 10; the length of structure 35 is 20; the length of structure 36 is 20; the length of structure 37 is 10;

[0056] Attached Figure 5 The dimensions of the structure are:

[0057] The length of structure 38 is 40; the length of structure 39 is 5; the diameter of structure 40 is 3; the diameter of structure 41 is 3;

[0058] The thickness of the silicon substrate is 15=100; the thickness of the metal layer of the microstrip line and the metal ground is 1; the width of the microstrip line is 70; under this structural size, the high capacitance ratio metal parallel MEMS switch operates below 180GHz and can ensure that the isolation in the off state is higher than 30dB; the insertion loss in the on state is lower than 0.8dB.

[0059] Attached Figure 6 The overall structure of a high capacitance ratio MEMS switch. 3D image

[0060] When the switch is in the off state, the return loss S 11 , Isolation S 21 The curve is as follows Figure 7 and attached Fig. 9 As shown:

[0061] Figure 7 and Fig. 9 The figure shows the return loss S of the high capacitance ratio MEMS switch in the off state. 11 , Isolation S 21 From the curve graph, it can be seen that the return loss of the switch in the range of 100-170GHz is significantly higher than -0.65dB and S21 is significantly less than -30dB.

[0062] When the switch is in the on state, the return loss S 11 , Insertion loss S 21 The curve is as follows Figure 8 and attached Fig.10 As shown:

[0063] Figure 8 and Fig.10 The figure shows the return loss S of the high capacitance ratio MEMS switch in the on state. 11 , Insertion loss S 21 From the curve graph, it can be seen that the return loss of the switch in the range of 100-170GHz is significantly higher than -15dB, and the insertion loss S21 is significantly higher than -0.80dB.

[0064] The switch has a driving voltage of 10-15V and a response speed of microseconds.

[0065] In summary, the present invention designs a metal parallel switch with a high capacitance ratio which can be used as a switch unit on a phased array or a RIS transmitting array, and the switch has good isolation and loss characteristics in the terahertz band.

[0066] The above is only an example. If you want to obtain a metal parallel MEMS switch that works at different frequencies, you can design different switch sizes for application in different scenarios.

Claims

1. A metal parallel RF MEMS switch with a high capacitance ratio in the terahertz band, comprising a coplanar waveguide metal ground (14), a silicon-based substrate (15) and a metal ground (42), wherein the coplanar waveguide metal ground (14) is located on the upper surface of the silicon-based substrate (15); and the metal ground (42) is located on the lower surface of the silicon-based substrate (15); characterized in that: It also includes a DC port metal block, a DC bias line, a microstrip line matching structure (13) and a metal beam MEMS switch; the DC port metal block, the microstrip line matching structure (13) and the metal electrodes of the metal beam MEMS switch are all located on the upper surface of the silicon-based substrate (15); The microstrip line matching structure (13) is located in an area surrounded by a coplanar waveguide metal ground, and a silicon nitride film is arranged in the middle of the area; The bridge piers on both sides of the metal beam MEMS switch are located on the coplanar waveguide metal ground and are placed directly above the silicon nitride film; there are two groups of DC port metal blocks, both groups of DC port metal blocks are located outside the area surrounded by the coplanar waveguide metal ground, one group of DC port metal blocks is connected to the coplanar waveguide metal ground, and the other DC port metal block is connected to the metal electrode of the metal beam MEMS switch through a DC bias line.

2. The terahertz band high capacitance ratio metal parallel RF MEMS switch according to claim 1, characterized in that: The metal beam MEMS switch includes a left bridge pier, a left folding arm, a left action arm, a left middle arm, an H-shaped structure, a right middle arm, a right action arm, a right folding arm and a right bridge pier, which are connected from left to right in sequence; wherein the left action arm, the left middle arm, the right action arm and the middle arm are all corroded with periodic circular holes; and the intermediate conduction structure of the H-shaped structure micro metal beam MEMS switch.

3. The terahertz band high capacitance ratio metal parallel RF MEMS switch according to claim 1, characterized in that: The middle conduction structure of the metal beam MEMS switch is an H-type structure. There are two cylindrical contacts on both sides of the lower surface of the H-type structure. The H-type structure is suspended directly above the silicon nitride film. When the metal beam MEMS switch is closed, the cylindrical contacts are in contact with the upper surface of the silicon nitride film.

4. The metal parallel RF MEMS switch with high capacitance ratio in the terahertz band according to claim 1, characterized in that: The microstrip line matching structure (13) is symmetrical about its center, and is composed of input and output microstrip lines and an intermediate trapezoidal gradient matching structure connected to the inner ends thereof, and is used for matching; the intermediate conduction (18) structure of the metal beam MEMS switch (11) is located directly above the intermediate trapezoidal gradient matching structure, and conduction is achieved when the intermediate conduction structure of the metal beam MEMS switch (11) is suspended in the air.

5. The metal parallel RF MEMS switch with high capacitance ratio in the terahertz band according to claim 1, characterized in that: The upper surfaces of the metal electrodes of the metal beam MEMS switch (11) are provided with a silicon nitride insulating layer, and the two metal electrodes correspond to the left action arm and the right action arm respectively. The metal electrodes are located directly below the corresponding action arms to pull down the action arms when power is turned on.

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