A metal parallel type RF MEMS switch with high capacitance ratio in terahertz wave band

Abstract

The application discloses a metal parallel type RF MEMS switch with 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 DC bias line, a microstrip line matching structure, a metal beam MEMS switch, a metal electrode of the metal beam, a silicon nitride insulating layer, a silicon substrate, a co-planar waveguide metal ground and a metal ground. The metal anchor point of the metal beam is connected to the co-planar waveguide metal ground, the DC port on the upper right side is connected to the co-planar waveguide metal ground through the DC bias line, the DC port on the upper left side is connected to the metal electrode through the DC bias line, the state of lifting and adsorbing of the metal beam to the electrode can be controlled by inputting different DC voltages at the DC port on the left side, and the switch is correspondingly in the on state and the off state; the parallel MEMS switch designed in the application works between 103.33G-170G, the isolation degree in the off state is higher than 33.67dB, and the insertion loss in the on state is lower than 0.8dB. The reaction time is in the order of microseconds, destructive deformation is not prone to occur, and the structure is simple.

Description

TECHNICAL FIELD

[0001] The application relates to a high-capacitance-ratio metal parallel RF MEMS switch design mainly applied to a satellite communication system in a terahertz frequency band and belonging to the field of radio frequency front-end devices. BACKGROUND

[0002] The essence of the radio frequency MEMS switch is to efficiently and accurately control the on-off state of a circuit. Compared with the traditional PIN diode switch or variable capacitance diode switch, the radio frequency MEMS switch has the advantages of small size, light weight, insensitivity to acceleration, no direct current loss at the microwave frequency, high isolation, low power consumption and low insertion loss. For the communication system in the terahertz band, the traditional PIN diode switch or variable capacitance diode switch has the problems of too high loss characteristic, too low isolation, low linearity and the like at the high frequency band, and is not suitable for application to the communication system in the high frequency band. Therefore, the radio frequency MEMS switch has a wide application to the phased array antenna, the switch matrix of the satellite switching network, the reconfigurable antenna, the radar and the unmanned aerial vehicle in the high frequency band.

[0003] According to the existing theory of MEMS switch, the MEMS switch can be divided into active MEMS switch and passive MEMS switch according to the requirement of external power supply, the active MEMS switch includes electricity, machinery, photochemistry and similar energy field conversion into mechanical energy to produce displacement, and has good driving performance; the passive MEMS switch collects energy by using the structure itself as an inertial actuator, and has excellent storage efficiency and anti-electromagnetic wave interference capability; according to the different contact modes, the MEMS switch can be divided into capacitive MEMS and resistive MEMS, the capacitive MEMS switch is suitable for high frequency application above 30MHZ, and the on-off state of the circuit is realized by using capacitive coupling; the resistive MEMS switch is suitable for low frequency application of 30kHZ-300kHz; the MEMS switch can also be divided into silicon-based switch and non-silicon-based switch according to the different processing materials, the silicon-based switch has high resistance, and large insertion loss is generated in the application process, and the non-silicon-based switch is mainly a metal switch, the metal switch can solve the problem of large contact resistance, but the microstructure of metal has not yet matured, and the switch may be deformed in the manufacturing process, therefore, the product yield is low. In the published works, there are few MEMS switches applied in the terahertz high frequency band and having high isolation, low insertion loss and low power consumption. In 2016, Theodore Reck et al. proposed a radio frequency MEMS waveguide reflection switch working at 700GHZ, and realized an isolation of more than 20dB and an insertion loss of 3dB in the whole frequency band, and the insertion loss is high; in 2017, Feng Yukang and Scott Barker proposed a radio frequency MEMS direct contact switch working at 500-750GHZ, and realized an isolation of 17-22dB and an insertion loss of 1.3-2.65dB, the insertion loss is high, and the switch is made on high resistance silicon as a waveguide switch, and is not easy to integrate.

[0004] In summary, there are few MEMS switches working in the terahertz band at present, and most of them do not have good insertion loss characteristics, and cannot meet the requirements of communication equipment application in the terahertz band. SUMMARY

[0005] In order to solve the problems in the background art, the present application provides a metal parallel RF MEMS switch with high capacitance ratio in the terahertz band. The RF MEMS switch uses the floating metal film in the on structure to improve the capacitance of the switch, realizes 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 application is realized by the following technical scheme:

[0007] The application discloses a metal parallel type RF MEMS switch with high capacitance ratio in a terahertz wave band, which comprises 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; the metal parallel type RF MEMS switch further comprises 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 a region surrounded by the coplanar waveguide metal ground, and a silicon nitride film is arranged at the middle position of the microstrip line matching structure 13.

[0009] The two side piers of the metal beam MEMS switch are both located on the coplanar waveguide metal ground and are arranged directly above the silicon nitride film; the DC port metal block is provided with two groups, and the two groups of DC port metal blocks are both located outside the region surrounded by the coplanar waveguide metal ground, one group of the DC port metal blocks is connected with the coplanar waveguide metal ground, and the other group of the DC port metal blocks is connected with the metal electrodes of the metal beam MEMS switch.

[0010] Further, the metal beam MEMS switch comprises, sequentially from left to right, a left side pier, a left side folding arm, a left side action arm, a left middle arm, an H-shaped structure, a right side middle arm, a right side action arm, a right side folding arm and a right side pier; periodic circular holes are etched on the left side action arm, the left middle arm, the right side action arm and the middle arm; and the H-shaped structure is a middle conduction structure of the metal beam MEMS switch.

[0011] Further, the middle conduction structure of the metal beam MEMS switch is an H-shaped structure, two cylindrical contacts are distributed on the lower surface of the H-shaped structure, the H-shaped structure is suspended directly above the silicon nitride film, and the cylindrical contacts are in contact with the upper surface of the silicon nitride film when the metal beam MEMS switch is closed.

[0012] Further, the microstrip line matching structure 13 is symmetrical about the center thereof, is composed of an input / output microstrip line and an intermediate trapezoidal gradual matching structure connected with the inner end of the input / output microstrip line, and is used for matching; the middle conduction structure 18 of the metal beam MEMS switch 11 is located directly above the intermediate trapezoidal gradual matching structure, and the middle conduction structure of the metal beam MEMS switch 11 is suspended to realize conduction.

[0013] Further, the upper surfaces of the metal electrodes of the metal beam MEMS switch 11 are all provided with silicon nitride insulating layers, and the two metal electrodes correspond to the left side action arm and the right side action arm respectively; the metal electrodes are located directly below the corresponding action arms to realize the pulling down of the action arms when electricity is conducted.

[0014] Compared with the prior art, the application has the following advantages:

[0015] a) The structure is simple, easy to manufacture, and can be applied to phased array antennas, super surface reflection array antennas and other radio frequency circuits to control the on and off of the switch.

[0016] b) The H-shaped floating metal film under the H-shaped metal sheet in the middle of the metal beam can effectively block the flow of signals.

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

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

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

[0020] Figure 2 is a structure diagram of the overall structure of the present application in the off state;

[0021] Figure 3 is a structure diagram of the overall structure of the present application in the on state;

[0022] Figure 4 is a structure diagram of the metal beam MEMS switch in the present application;

[0023] Figure 5 is a structure diagram of the middle on structure of the metal beam MEMS switch in the present application;

[0024] Figure 6 is a three-dimensional view of the overall structure of the present application;

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

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

[0027] Figure 9 is the return loss S of the metal parallel MEMS switch in the off state of the present application 11 curve;

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

[0029] The following will be described in conjunction with the accompanying Figures 1-8The specific embodiments of the present application are further described in detail with reference to the examples.

[0030] A metal parallel type RF MEMS switch with high capacitance ratio in a terahertz wave 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 co-planar 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] The DC port metal block has a total of 2, which are divided into two groups; the two groups of DC port metal blocks are both located on the left side of the microstrip line matching structure, and the metal beam MEMS switch is arranged between the two groups of DC port metal blocks and the microstrip line matching structure; the metal beam MEMS switch is all located above the microstrip line matching structure.

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

[0033] The metal beam MEMS switch comprises, sequentially from left to right, a left side pier, a left side folded arm, a left side action arm, a left middle arm, an H-shaped structure, a right side middle arm, a right side action arm, a right side folded arm and a right side pier; periodic circular holes are etched on the left side action arm, the left middle arm, the right side action arm and the middle arm.

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

[0035] The microstrip line matching structure is composed of an input / output microstrip line and an intermediate trapezoidal gradual matching structure connected to the inner end of the input / output microstrip line, and is used for matching; the middle conduction structure of the metal beam MEMS switch is located directly above the intermediate trapezoidal gradual matching structure, and conduction is realized when the middle conduction structure of the metal beam MEMS switch is stationary.

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

[0037] The accompanying drawings are included to provide a further understanding of the present application, and are incorporated herein and constitute a part of the detailed description. Figure 1 The accompanying drawings are included to provide a further understanding of the present application, and are incorporated herein and constitute a part of the detailed description. Figure 6A metal parallel type RF MEMS switch with high capacitance ratio in the terahertz band is taken as an example, the embodiment includes DC port metal block 1, 2, DC bias line 3, 4, 5, microstrip line matching structure 13, metal beam MEMS switch pier 11, 12, metal beam middle conduction structure 18, metal beam metal electrode 20, 22, silicon nitride insulating layer 17, 19 on the upper surface of the metal electrode of the metal beam, silicon-based substrate 15, coplanar waveguide metal ground 14, metal ground 42; Because the ordinary metal beam MEMS switch has poor performance, it can cause low isolation, so a floating metal film is added below the transmission line to improve the isolation of the switch, and the metal beam is directly composed of a fixed beam with H-shaped structure as the symmetry. The metal beam and the metal electrodes 20, 22 distributed on both sides below the metal beam are connected to the same side DC port metal block 1 through the DC bias line 3, 4.

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

[0039] The overall structure is in the off state as shown in FIG. 1 Figure 3 The DC port metal block 2 is grounded or has the same voltage, and the metal beam switch passes through the DC port metal block 1 to ground the metal beam and the metal electrode and apply a driving voltage, the driving voltage generates an electrostatic force between the metal electrode and the metal beam, the metal beam 12 generates longitudinal deformation, the metal beam is pulled down as a whole, and finally the contact below the middle conduction structure 18 of the metal beam switch is in contact with the microstrip line matching structure 13 above, so that the overall structure is in the off state; if the switch is in the on state, as shown in FIG. 2 Figure 2 The DC port metal block 2 is grounded or has the same voltage, and the DC port metal block 1 is not connected to the voltage, at this time the metal beam switch 12 does not generate deformation, the middle conduction structure 18 of the metal beam switch is located directly above the microstrip line 13, and the two do not generate contact, at this time the signal is directly transmitted from the microstrip line to the other port, finally making the overall structure in the on state.

[0040] As shown in FIG. 3 Figure 4 The metal beam is a symmetrical structure composed of rectangular structures of different sizes including rectangular ring 28, folded arms (30, 31, 32, 33), connecting arm 35, action arm 37, and 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 the same as that of the connecting arm 35.

[0041] The above design of the metal parallel type based on the floating metal film is to improve the isolation 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, have a shorter response time, reduce the residual stress, and realize the high-speed and reliable performance of the switch. The driving voltage of the present embodiment can be controlled at 10-15V.

[0042] As shown in the accompanying drawings Figure 5 The middle conduction structure 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 structure design is to increase the isolation of the switch, reduce the insertion loss and power consumption of the switch.

[0043] The accompanying drawings Figures 7 to 10 The scattering parameter curves of the insertion loss S11 and the isolation S21 performance of the switch in the off and on states, respectively.

[0044] The size parameters of the middle conduction structure and the microstrip line matching structure will affect the radio frequency performance of the switch, the size of the metal beam and the metal electrode will affect the driving voltage, etc. The main performance is:

[0045] A. The narrower the overall width of the middle conduction structure, the better the isolation of the switch in the off state. The switch in this design adopts a metal parallel type, and the H-shaped floating metal film is below the middle conduction structure. By adjusting the size of the conduction structure and the size of the floating metal film, the isolation can be optimized.

[0046] B. The longer the overall length of the switch and the longer the off length of the microstrip line matching structure, the better the isolation of the switch and the lower the driving voltage, but it will increase the possibility of destructive deformation of the switch, which will reduce the reliability of the switch, and also increase the overall size of the switch structure, affecting the layout and use.

[0047] C. The size of the microstrip line matching structure will affect the switch loss characteristics 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 of the switch in the on state.

[0048] D. The size of the metal beam switch mainly affects the driving voltage and response time performance. This design uses a folding structure, and by continuously optimizing the size of the rectangular ring, the connecting arm, the action arm and the H-shaped structure, the working voltage of the driving voltage is stabilized between 10-15V, and the response time is in the order of microseconds.

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

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

[0051] The following selects a size combination to introduce the size of the structure in the drawings. The following data unit is microns;

[0052] Figure 2 The size of the structure is:

[0053] The length of structure 16 is 10; the side length of the silicon nitride insulation layer 17, 19 of the electrode 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 under the middle conduction structure 18 of the metal beam is = 3; the thickness of the silicon nitride insulation layer is = 0.1;

[0054] As shown in the accompanying drawings 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] As shown in the accompanying drawings 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-based substrate 15 is 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 structure size, the high-capacitance-ratio metal parallel MEMS switch works below 180GHz, and all 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] As shown in the accompanying drawings Figure 6 is a three-dimensional image of the overall structure of the high-capacitance-ratio MEMS switch

[0060] When the switch is in the off state, the return loss S 11 , the isolation S 21 curve as shown in the accompanying drawings Figure 7 and Figure 9 :

[0061] Figure 7 and Figure 9 The curves shown in FIGS. 1 and 2 are the return loss S 11 , the isolation S 21 of the high-capacitance-ratio MEMS switch in the off state, and it can be seen that the return loss of the switch is obviously higher than -0.65dB and S21 is significantly less than -30dB in the range of 100-170GHz.

[0062] When the switch is in the on state, the return loss S 11 , the insertion loss S 21 curve as shown in the accompanying drawings Figure 8 and Figure 10 :

[0063] Figure 8 and Figure 10 The curve diagram of return loss S 11 , insertion loss S 21 of the high-capacitance-ratio MEMS switch in the on state is shown in Figure 2, and it can be seen that the return loss of the switch is obviously higher than -15 dB and the insertion loss S21 is obviously higher than -0.80 dB in the range of 100-170 GHz.

[0064] The driving voltage of the switch is 10-15 V, and the response speed is in the order of microseconds.

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

[0066] The above is only an example, and if a metal parallel MEMS switch working at different frequencies is needed, different switch sizes can be designed so as to be applied 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 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); The microstrip line matching structure (13) is located in an area surrounded by a coplanar waveguide metal ground, and a silicon nitride film is provided 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 of which 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 in sequence from left to right. The left action arm, the left middle arm, the right action arm and the middle arm are all etched with periodic circular holes. The H-shaped structure is the middle conductive structure of the 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-shaped structure. There are two cylindrical contacts on each side of the lower surface of the H-shaped structure. The H-shaped structure is suspended directly above the silicon nitride film. When the metal beam MEMS switch is closed, the cylindrical contacts contact the upper surface of the silicon nitride film.

4. The terahertz band high capacitance ratio metal parallel RF MEMS switch according to claim 1, characterized in that: The microstrip line matching structure (13) is symmetrical about its center and consists 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 (18) 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 terahertz band high capacitance ratio metal parallel RF MEMS switch according to claim 1, characterized in that: The upper surfaces of the metal electrodes of the metal beam MEMS switch (11) are both 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, so as to pull down the action arms when power is turned on.

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