Terahertz wave band parallel capacitor type RF MEMS switch

Abstract

The invention discloses a terahertz wave band parallel capacitance type RF MEMS switch, and belongs to the field of radio frequency front-end devices. The device is composed of a direct current port metal block, a direct current bias line, a microstrip line matching structure, a metal beam MEMS switch, a metal beam middle contact structure, a metal electrode of a metal beam, a silicon nitride insulating layer, a quartz glass substrate, a coplanar waveguide metal ground and a metal ground. The direct current ports are respectively connected to a metal beam pier position and a metal electrode through direct current bias lines, a bridge is arranged in the middle of the coplanar waveguide metal ground, the direct current bias lines pass through the lower portion of the bridge, a silicon nitride insulating layer is arranged on the upper surface of each direct current bias line, devices are prevented from being damaged by short circuit, and a zigzag structure is properly introduced to prevent leakage of radio frequency signals. The metal beam MEMS switch designed by the invention realizes low driving voltage, low insertion loss, high isolation and microsecond-order reaction time, is not easy to cause destructive deformation, and is simple in structure and easy to manufacture.

Description

TECHNICAL FIELD

[0001] The application relates to a design of a parallel capacitance type RF MEMS switch in a terahertz wave band, which is mainly applied to a satellite communication system in a terahertz frequency band and belongs to the field of radio frequency front-end devices. BACKGROUND

[0002] RF MEMS is an important branch of MEMS technology in the field of radio frequency. By using MEMS technology to manufacture RF devices, components or subsystems, the functions of RF signal acquisition, transmission and processing are realized, and advantages such as miniaturization, low power consumption, low cost and integration are gradually widely applied in military and civilian fields.

[0003] According to the driving mode of the mechanical structure of the MEMS switch, the switch can be divided into electrostatic driving, electromagnetic driving, electrothermal driving and piezoelectric driving. The electrostatic driving mode is relatively mature, and is the most widely researched and the most commonly used driving mechanism. According to the contact mode of the switch, it can be divided into ohmic contact type and capacitive coupling type. According to the manufacturing material of the MEMS switch, it can be divided into non-quartz glass switch and quartz glass switch. Quartz glass material often has high resistance and high insertion loss. At present, there are few MEMS switches with high integration, high isolation, low insertion loss and high linearity in the field of radio frequency. For example, Rahul Gogna et al. proposed a MEMS switch working in the terahertz wave band in 2016. It has high integration and can be applied to coplanar waveguide and other transmission line structures. In the frequency range of 180-250GHz, the return loss is realized to be 24-12dB, but the insertion loss is as high as 1.2-2.7dB.

[0004] In summary, there are few MEMS switches working in the terahertz wave 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 frequency band. SUMMARY

[0005] In order to solve the problems in the background art, the application provides a parallel capacitance type RF MEMS switch in a terahertz wave band. The metal beam MEMS switch has the characteristics of simple structure, high isolation, low insertion loss, low power consumption and difficulty in generating structural deformation, and can be used in the terahertz wave band.

[0006] In order to solve the above technical problems, the application is realized by the following technical scheme: A parallel capacitance type RF MEMS switch in a terahertz wave band comprises a MEMS switch, a quartz glass substrate, a coplanar waveguide metal ground and a metal ground. Its characteristics further comprise a direct current port metal block, a direct current bias line and a microstrip line matching structure. The coplanar waveguide metal ground is located on the upper surface of the quartz glass substrate; the metal ground is located on the lower surface of the quartz glass substrate; the center of the coplanar waveguide metal ground is provided with a rectangular hollow, and the MEMS switch and the microstrip line matching structure are located in the rectangular hollow; The MEMS switch is located at the middle position of the microstrip line matching structure, and the metal electrode and the abutment of the MEMS switch are connected with the DC port metal block through the corresponding DC bias line; the DC bias line corresponding to the metal electrode passes through the bridge of the coplanar waveguide metal ground and is connected with the DC port metal block and the corresponding DC bias line in the form of a meandering structure outside the bridge. The DC bias line under the bridge is covered with a bridge-under insulation layer.

[0007] Further, the microstrip line matching structure is a tapered structure with a narrow middle part and wide ends, and the two ends of the microstrip line matching structure are connected with the wide sides of the rectangular hollow in the coplanar waveguide metal ground through the corresponding excitation port. The two abutments of the MEMS switch are located at the edge positions of the coplanar waveguide metal ground and are respectively located on both sides of the middle part of the microstrip line matching structure; the metal electrode is located in the rectangular hollow and is respectively located between the corresponding abutment and the microstrip line matching structure.

[0008] Further, the middle position of the coplanar waveguide metal ground is provided with a gap, and the gap penetrates into the rectangular hollow; the coplanar waveguide metal ground separated by the gap is connected through the bridge; the gap is located below the corresponding bridge.

[0009] Further, the MEMS switch comprises a metal beam, a middle contact structure, two metal electrodes and two abutments. The two ends of the metal beam are respectively connected to the top of the two abutments, and span the middle position of the microstrip line matching structure; the middle contact structure is located at the middle position of the bridge and corresponds to the middle part of the microstrip line matching structure directly below it. The middle part of the microstrip line matching structure is provided with a middle silicon nitride insulation layer on the top.

[0010] Further, the metal beam is a symmetrical structure with the middle contact structure as the middle line, comprising a left connecting arm, a left action arm, a left middle arm, a middle contact structure, a right middle arm, a right action arm and a right connecting arm connected in sequence from left to right; periodic square holes are etched on the left action arm, the left middle arm, the right middle arm and the right action arm. The two metal electrodes are respectively located directly below the left action arm and the right action arm, and a silicon nitride insulation layer is provided above each of them.

[0011] Further, the two abutments are connected to the corresponding DC port metal block through the coplanar waveguide metal ground and the corresponding DC bias line; the two metal electrodes are connected to the corresponding DC port metal block through the corresponding DC bias line.

[0012] Further, the material of the metal beam is gold.

[0013] Further, the middle contact structure of the MEMS switch is a rectangular metal contact patch.

[0014] Further, the microstrip line matching structure is used for matching, and is opposite to the middle contact structure of the MEMS switch, and realizes the switch-off state when pulled down.

[0015] Compared with the background art, the present application has the following advantages: a. The switch structure is simple and convenient to manufacture, and can be applied to radio frequency circuits such as phased array antennas, super surface reflection array antennas, etc., to control the on and off states.

[0016] b. The switch-off state has high isolation, and the on state has low insertion loss.

[0017] c. The switch uses a metal beam structure, which can work at a low driving voltage, has a short response time, high reliability, and is not easy to break during work. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a top view of the overall structure of the present application; Figure 2 is a structure diagram of the upper surface of the quartz glass substrate of the present application; Figure 3 is a structure diagram of the on state of the present application; Figure 4 is a structure diagram of the off state of the present application; Figure 5 is a bottom view of the middle contact structure of the metal beam MEMS switch in the present application; Figure 6 is a structure diagram of the metal beam MEMS switch in the present application; Figure 7 is a three-dimensional perspective view of the overall structure of the present application; Figure 8 is a return loss S 11 , isolation S 21 curve of the off state of the metal beam MEMS switch in the present application; Figure 9 is a return loss S 11 , insertion loss S 21 curve of the on state of the metal beam MEMS switch in the present application.

[0019] In the figure: 1, DC port metal a block, 2, DC port metal b block, 3, DC bias a line, 4, DC bias b line, 5, DC bias c line, 6, DC bias d line, 7, DC bias e line, 8, microstrip line matching structure, 9, coplanar waveguide metal ground, 10, excitation a port, 11, excitation b port, 12, metal beam, 13, quartz glass substrate, 14, left metal electrode, 15, right metal electrode, 16, left abutment, 17, right abutment, 18, metal ground, 19, middle contact structure, 20, left silicon nitride insulating layer, 21, middle silicon nitride insulating layer, 22, right silicon nitride insulating layer, 23, left bridge, 24, right bridge, 25, left insulating layer under the bridge, 26, right insulating layer under the bridge, 33, left connecting arm, 34, left action arm, 35, left middle arm, 36, right middle arm, 37, right action arm, 38, right connecting arm. DETAILED DESCRIPTION

[0020] The specific embodiments of the present application are described below in conjunction with the accompanying drawings. Figures 1-9 The specific embodiments of the present application are described below in conjunction with the accompanying drawings.

[0021] The present embodiment provides a parallel capacitance type RF MEMS switch in the terahertz wave band, and its structural components and positional relationship are as follows: The quartz glass substrate 13 is used as the substrate of the device, and its dielectric constant is 3.78 and its thickness is 100 microns. The coplanar waveguide metal ground 9 is located on the upper surface of the substrate and has a rectangular hollow area in the center. The metal ground 18 is located on the lower surface of the substrate and is used to provide overall grounding and shielding.

[0022] The microstrip line matching structure 8 is located in the center of the rectangular hollow area of the coplanar waveguide metal ground 9 and has a tapered form with a narrow middle and wide ends. The two ends of the microstrip line matching structure 8 are connected to the coplanar waveguide metal ground 9 through the excitation a port 10 and the excitation b port 11 respectively. The upper surface of the middle part of the microstrip line matching structure 8 is provided with the middle silicon nitride insulating layer 21.

[0023] The MEMS switch includes the metal beam 12, the middle contact structure 19, the left metal electrode 14, the right metal electrode 15, the left abutment 16 and the right abutment 17. The two ends of the metal beam 12 are fixed on the left abutment 16 and the right abutment 17 respectively and span above the middle part of the microstrip line matching structure 8. The metal beam 12 is made of gold and has a symmetrical structure, which includes, from left to right, the left connecting arm 33, the left action arm 34, the left middle arm 35, the middle contact structure 19, the right middle arm 36, the right action arm 37 and the right connecting arm 38. Periodic square holes are etched on the left action arm 34, the left middle arm 35, the right middle arm 36 and the right action arm 37. The middle contact structure 19 is a rectangular metal contact pad located below the center of the bridge.

[0024] The left metal electrode 14 is located directly below the left moving arm 34, and the upper surface is covered with a left silicon nitride insulating layer 20. The right metal electrode 15 is located directly below the right moving arm 37, and the upper surface is covered with a right silicon nitride insulating layer 22.

[0025] The left metal electrode 14 and the right metal electrode 15 are connected to the DC port metal a block 1 through the DC bias a line 3, the DC bias b line 4, the DC bias c line 5, and the DC bias d line 6. The left bridge 16 and the right bridge 17 are connected to the DC port metal b block 2 through the DC bias e line 7.

[0026] The coplanar waveguide metal ground 9 is provided with a gap at the middle position, dividing the metal ground 18 into two parts, and the two parts are connected through the left bridge 23 and the right bridge 24. The DC bias a line 3 passes below the left bridge 23, and the upper surface is covered with a left bridge lower insulating layer 25. The DC bias b line 4 passes below the right bridge 24, and the upper surface is covered with a right bridge lower insulating layer 26. The DC bias a line 3 and the DC bias b line 4 extend to the DC port metal a block 1 in a meandering structure with multiple bends.

[0027] The MEMS switch adopts an electrostatic driving mode, and the conduction and disconnection of the switch are realized by controlling the voltage of the DC port metal a block 1 and the DC port metal b block 2.

[0028] When the DC port metal a block 1 and the DC port metal b block 2 are both grounded or the same voltage is applied, the MEMS switch as a whole does not produce longitudinal deformation, the bridge remains in the original position, and there is no contact between the middle contact structure 19 and the microstrip line matching structure 8. At this time, the radio frequency signal can be transmitted along the microstrip line matching structure 8 with low loss, realizing the conduction state of the switch.

[0029] When a driving voltage is applied between the DC port metal a block 1 and the DC port metal b block 2, electrostatic force is generated between the left metal electrode 14, the right metal electrode 15, and the metal beam 12, attracting the metal beam 12 to bend downward, so that the rectangular metal contact patch of the middle contact structure 19 contacts the middle silicon nitride insulating layer 21 on the microstrip line matching structure 8, forming a capacitive coupling, resulting in a short circuit of the radio frequency signal to ground, thereby realizing a high-isolation disconnected state of the switch.

[0030] The purpose of the above-mentioned metal beam 12 structure design is to reduce the pull-down driving voltage, have a shorter response time, reduce residual stress, and realize high-speed and reliable performance of the switch. In the present embodiment, the driving voltage can be controlled to be 25-35V.

[0031] As shown in FIG. 3 and FIG. 4, the switch is in the disconnected state and the conduction state, respectively. Figure 8 and FIG. 4 are the return loss S11 and S21 performance scattering parameter curves of the switch in the disconnected and conduction states, respectively. Figure 9

[0032] ​The dimensions of the intermediate contact structure (19) and the microstrip line matching structure (8) affect the switching RF performance. The dimensions of the metal beam (12) and metal electrodes affect the magnitude of the drive voltage and other performance characteristics, mainly manifested as follows: A. The larger the area of ​​the intermediate contact structure 19, the greater the isolation in the open state of the switch. This design uses a rectangular metal contact piece, adjusts the detailed dimensions, and optimizes the isolation.

[0033] B. The longer the overall width of the switch, the better the isolation of the switch, but it will increase the overall size of the switch structure and affect the layout and use.

[0034] C. The size of the microstrip line matching structure 8 affects the switching loss characteristics when the switch is in the on state. This design adopts a gradient structure from the microstrip line width to the width of the conduction structure, which helps to reduce the insertion loss when the switch is in the on state.

[0035] D. The dimensions of the metal beam 12 mainly affect the performance of the driving voltage and response time. This design adopts a fixed support beam structure switch with a hollow center, and by continuously optimizing the dimensions of the connecting arm, the action arm and the intermediate contact structure 19, the working voltage of the driving voltage is stabilized between 25-35V and the response time is in the microsecond range.

[0036] E. The size and spacing of the periodic square holes will affect the magnitude of the electrostatic force between the metal electrode and the metal beam 12, and thus also affect the magnitude of the working voltage of the driving voltage.

[0037] Therefore, selecting the appropriate metal beam size 12, intermediate contact structure size 19, and microstrip line matching structure size 8 is crucial for improving the overall switching performance.

[0038] The following section uses a combination of dimensions to illustrate the size of the structure in the attached diagram. The data below is in micrometers. Appendix Figure 3 The dimensions of the structure are: The length of a is 1; the length of b is 1.6; the length of c is 0.5; the length of d is 0.5; the length of e is 0.5; the length of f is 0.3; the rectangular metal contact piece of the middle contact structure is 19×15 in length and width.

[0039] Appendix Figures 5-6 The dimensions of the structure are: The length of g is 40; the length of h is 15; the length of i is 10; the length of j is 35; the length of k is 30; the length of l is 20; the length of m is equal to the length of o, both of which are 10; the length of n is 20; the side length of the periodic square hole structure p is 4.

[0040] The thickness of the quartz glass substrate 13 is 100; the thickness of the microstrip line matching structure 8 and the coplanar waveguide metal ground 9 is 0.5; the width of the microstrip line matching structure 8 is 80; and the thickness of the silicon nitride insulation layer is 0.1. Under the structure size, the switch can work at 140GHz, and the isolation in the off state is higher than 35dB, and the insertion loss in the on state is lower than 0.3dB.

[0041] The accompanying drawings are included to provide a further understanding of the present application, and are incorporated herein and constitute a part of this application. Figure 7 It is a three-dimensional image of the overall structure of the MEMS switch.

[0042] When the switch is in the off state, the return loss S11 and the isolation S21 curves are as shown in the accompanying drawings. Figure 8 It can be seen that the return loss S11 of the switch is higher than -0.3dB, and the isolation S21 is between -23dB and -50dB in the range of 110-165GHz.

[0043] When the switch is in the on state, the return loss S11 and the insertion loss S21 curves are as shown in the accompanying drawings. Figure 9 It can be seen that the return loss S11 of the switch is lower than -10dB, and the insertion loss S21 is between -0.2dB and -1.2dB in the range of 110-165GHz.

[0044] The driving voltage of the switch is 25-35V, and the response speed is in the order of microseconds.

[0045] In summary, the MEMS switch provided by the present application can be integrated into a microstrip line or a coplanar waveguide transmission line, and has good isolation and loss characteristics in the terahertz wave band.

[0046] The above is only an example, and if a MEMS switch working at different frequencies is needed, different switch sizes can be designed to be applied in different scenarios.

Claims

1. A THz band parallel-plate RF MEMS switch comprising a MEMS switch, a quartz glass substrate (13), a coplanar waveguide metal ground (9) and a metal ground (18); characterized in that, Also includes DC port metal block, DC bias line and microstrip line matching structure (8); The coplanar waveguide metal ground (9) is located on the upper surface of the quartz glass substrate (13); the metal ground (18) is located on the lower surface of the quartz glass substrate (13); the center of the coplanar waveguide metal ground (9) is provided with a rectangular hollow, and the MEMS switch and the microstrip line matching structure (8) are located in the rectangular hollow; Wherein, the MEMS switch is located at the middle position of the microstrip line matching structure (8), the metal electrode of the MEMS switch and the pier are connected with the DC port metal block through the corresponding DC bias line; the DC bias line corresponding to the metal electrode passes through the bridge of the coplanar waveguide metal ground and is connected with the DC port metal block and the corresponding DC bias line in the form of a tortuous structure by being bent multiple times outside the bridge. The DC bias line under the bridge is covered with an under-bridge insulating layer.

2. The parallel-plate capacitive RF MEMS switch of claim 1, wherein, The microstrip line matching structure (8) is a tapered structure with narrow middle and wide ends, and the two ends of the microstrip line matching structure are connected with the wide edges of the rectangular hollow in the coplanar waveguide metal ground (9) through the corresponding excitation ports. The two piers of the MEMS switch are located at the edge positions of the coplanar waveguide metal ground (9) and are respectively located on both sides of the middle part of the microstrip line matching structure (8); the metal electrode is located in the rectangular hollow and is respectively located between the corresponding pier and the microstrip line matching structure (8).

3. The parallel-plate capacitive RF MEMS switch of claim 1, wherein, The middle position of the coplanar waveguide metal ground (9) is provided with a gap, and the gap penetrates into the rectangular hollow; the coplanar waveguide metal ground (9) separated by the gap is connected through the bridge; the gap is located below the corresponding bridge.

4. The shunt capacitance RF MEMS switch of claim 2, wherein, The MEMS switch comprises a metal beam (12), a middle contact structure (19), two metal electrodes and two piers. The two ends of the metal beam (12) are respectively connected to the top of the two piers, and span the middle position of the microstrip line matching structure (8); the middle contact structure (19) is located at the middle position of the bridge and corresponds to the middle part of the microstrip line matching structure (8) directly below it; The middle part of the microstrip line matching structure (8) is provided with a middle silicon nitride insulating layer (21) on the top.

5. The shunt capacitance RF MEMS switch of claim 4, wherein, The metal beam (12) is a symmetrical structure with the middle contact structure (19) as the middle line, comprising a left connecting arm (33), a left action arm (34), a left middle arm (35), the middle contact structure (19), a right middle arm (36), a right action arm (37) and a right connecting arm (38) connected in sequence from left to right; wherein the left action arm (34), the left middle arm (35), the right middle arm (36) and the right action arm (37) are all etched with periodic square holes; Two metal electrodes are respectively located directly below the left action arm and the right action arm, and a silicon nitride insulating layer is provided above each of the two metal electrodes.

6. The shunt capacitance RF MEMS switch of claim 4, wherein, The two piers are connected with the corresponding DC port metal block through the coplanar waveguide metal ground (9) and the corresponding DC bias line; the two metal electrodes are connected with the corresponding DC port metal block through the corresponding DC bias line.

7. The shunt capacitance RF MEMS switch of claim 4, wherein, The material of the metal beam is gold.

8. The shunt capacitance RF MEMS switch of claim 4, wherein, The middle contact structure (19) of the MEMS switch is a rectangular metal contact patch.

9. The shunt capacitance RF MEMS switch of claim 1, wherein, The microstrip line matching structure (8) is used for matching and is opposite to the middle contact structure (19) of the MEMS switch, and realizes the switch-off state when pulled down.

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