Small terahertz mems spst switch based on common compound beam

Abstract

The application discloses a small terahertz MEMS single-pole four-throw switch based on a shared composite beam and belongs to the technical field of radio frequency MEMS. The single-pole four-throw switch based on the whole beam is composed of a microstrip main feeder, a bifurcated transition structure, a low-loss switch structure and a microstrip output line. The MEMS switch is formed into a high-isolation symmetric structure by a metal-dielectric whole composite beam, and the switch has a minimum size and a low pull-down voltage by combining a crane-shaped arm and a shared folding arm. The corresponding part of the beam is pulled down by electrostatic force generated by the potential difference between the bottom electrode and the shared beam metal part, and the metal contact on the beam makes the corresponding microstrip output line conductive. When one of the MEMS switch lines is turned on and the other lines are turned off, the signal transmission is completed. The reconfigurable switch is formed by four asymmetric single-pole single-throw switch units through symmetric and compact arrangement, has high isolation in an ultra-wide frequency band, has a channel reflection coefficient less than -15 dB in a DC-350 GHz frequency band, has an in-band insertion loss less than 1.8 dB, and has an isolation greater than 15 dB.

Description

Technical Field

[0001] This invention relates to a miniaturized terahertz MEMS single-pole four-throw switch based on a shared composite beam, which is mainly used in radio frequency systems in the terahertz band and belongs to the field of radio frequency MEMS technology. Background Technology

[0002] RF switches based on MEMS (Micro-Electro-Mechanical Systems) have wide and important applications in satellite communication front-ends, broadband network systems, and radar systems covering the microwave band due to their advantages such as wide operating bandwidth, high isolation, and low insertion loss. Research on low-frequency microwave MEMS switches is relatively abundant worldwide, mainly categorized into cantilever beam switches and fixed beam switches, high-power switches and low-power switches, and single-pole single-throw (SPS) switches and single-pole multi-throw (SMP) switches. Among these, SMP switches can switch RF signal paths with the fewest number of switching beams, providing a new dimension for simplifying control circuit design and enabling miniaturization of switching paths; however, the disadvantages of MEMS SMP switches include a low high-frequency cutoff frequency, difficulty in miniaturization, and significant impact on mechanical structural stability. Currently, research on terahertz band MEMS switches is limited, and no research on terahertz SMP switches has been published, posing significant challenges in the overall design of RF performance and mechanical structure. Existing high-frequency MEMS switches often require large beam sizes to achieve satisfactory RF performance, resulting in simple structures and unsatisfactory high-frequency throughput. For example, in 2011, N. Scott Barker et al. from the University of Virginia developed a cantilever beam-based direct-contact single-pole four-throw MEMS switch that could cover up to 75 GHz. Based on this switch, they developed a high-frequency phase shifter based on a switching line. However, the return loss of this switch was only 13 dB at 75 GHz. Subsequently, in 2016, Selin Tolunay Wipf published a paper in IEEE Microwave and Wireless Components Letters on a D-band single-pole double-throw MEMS switch fabricated using SiGeBiCMOS technology. The switch described in the paper could achieve an insertion loss of 1.42 dB and an isolation of 54.5 dB at 140 GHz, but the isolation deteriorated to 18.25 dB at 170 GHz, and the insertion loss also increased accordingly. In 2022, N. Scott Barker et al. designed a terahertz cantilever beam switch based on a coplanar waveguide using silicon and fused silica; however, a MEMS single-pole multi-throw switch operating at high-frequency terahertz has not yet been truly realized.

[0003] Current terahertz MEMS switches suffer from drawbacks such as large size, poor high-frequency isolation, and high losses, making them unsuitable for use in antennas and other RF devices. Furthermore, there is currently no research on miniaturization of terahertz MEMS switches specifically designed for single-pole multi-throw (SPMD) applications. Summary of the Invention

[0004] To address the problems existing in the background technology, this invention designs a miniature terahertz MEMS single-pole four-throw switch based on a shared composite beam, which can meet the requirements of terahertz frequency band RF path switching. The designed switch features miniaturization, high cutoff frequency, low insertion loss, and high isolation.

[0005] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0006] A miniaturized terahertz MEMS single-pole four-throw switch based on a shared composite fixed support beam includes a microstrip primary feed line 1, a trapezoidal protruding bifurcation structure 2, a voltage bias line group, an irregularly shaped MEMS switch, and microstrip secondary feed lines 20, 21, 22, and 23.

[0007] The trapezoidal protruding bifurcation structure 2 is mainly composed of a T-shaped power divider and two trapezoidal components. The two trapezoidal components correspond one-to-one with the two ends of the T-shaped power divider. The lower base of the trapezoidal component is close to one side of the end of the T-shaped power divider. The two trapezoidal components are located on the same side of the T-shaped power divider and are both opposite to the input end of the T-shaped power divider.

[0008] The output end of the microstrip primary feed line is connected to the input end of the T-junction power divider; the end of the T-junction power divider and the upper bottom edge of the trapezoidal component are connected to the microstrip secondary feed line one by one through irregularly shaped MEMS switches, and the irregularly shaped MEMS switches correspond one-to-one with the microstrip secondary feed line.

[0009] Four irregularly shaped MEMS switches share the same elastic dielectric membrane bridge 7. The metal bridge-shaped path and pull-down metal beam on each irregularly shaped MEMS switch are located on the lower surface of the elastic dielectric membrane bridge. The elastic dielectric membrane bridge and pull-down metal beam are supported and suspended by corresponding metal bridge piers, and a pull-down electrode is provided below the pull-down metal beam. The voltage bias line group is connected to the corresponding pull-down electrode and metal bridge pier. The two ends of the metal bridge-shaped path are respectively used to connect the microstrip primary feed line and the microstrip secondary feed line.

[0010] The metal bridge-shaped path and the pull-down metal beam on the same irregularly shaped MEMS switch are adjacent but not in contact.

[0011] Furthermore, the initial segment of the microstrip secondary feed line connected by the trapezoidal component is parallel to the microstrip primary feed line, and the microstrip secondary feed line connected to the end of the T-junction power divider is perpendicular to the microstrip primary feed line;

[0012] Among them, the two microstrip secondary feed lines connected by trapezoidal components are both bent at 135° and set opposite each other.

[0013] Furthermore, the elastic dielectric membrane bridge portion above the metal bridge-shaped passage is perpendicular to the long side of the metal bridge-shaped passage.

[0014] Furthermore, the two irregularly shaped MEMS switches corresponding to the trapezoidal components share a pull-down metal bridge, which has a H-shaped structure.

[0015] The pull-down metal bridges of the two irregularly shaped MEMS switches corresponding to the T-junction power divider are both U-shaped structures.

[0016] Furthermore, a high-frequency, low-loss dielectric material is used as the substrate; a corrosion-resistant, low-resistivity metal material is used as the metal beam; a compound dielectric material with a low elastic coefficient is used as the dielectric membrane bridge; the metal beam is fabricated using a sacrificial layer technique, and the dielectric membrane bridge is tightly bonded to the metal beam, allowing the dielectric membrane bridge to be driven by the downward pull of the metal beam.

[0017] Furthermore, the microstrip primary feed line, the microstrip secondary feed line, and the voltage bias line group together form a star-shaped configuration.

[0018] Compared with the prior art, the advantages of the present invention are:

[0019] a) This invention can achieve four-way RF signal switching in the terahertz band, avoiding the additional losses and mismatch problems introduced by the cascading of single-pole single-throw and double-throw switches;

[0020] b) The switch structure of the present invention is small in size, much smaller than that of traditional MEMS switches, and can be easily integrated into radio frequency systems with high density.

[0021] c) This invention exhibits stable performance over a wide terahertz frequency band, low insertion loss, high switching isolation, wide applicability, and is not difficult to manufacture. Attached Figure Description

[0022] Figure 1 This is a planar structural diagram of the switch portion according to an embodiment of the present invention;

[0023] Figure 2 This is a perspective view of the pull-down structure according to an embodiment of the present invention;

[0024] Figure 3 This is a process side view of an embodiment of the present invention;

[0025] Figure 4 This is a schematic diagram of the overall structure of the switchboard according to an embodiment of the present invention;

[0026] Figure 5 This is a state S-parameter curve diagram of an embodiment of the present invention;

[0027] Figure 6 This is a two-state S-parameter curve diagram of an embodiment of the present invention; Detailed Implementation

[0028] The following further elaborates on the specific implementation manners of the present invention in conjunction with the accompanying Figure 1-6 drawings and embodiments.

[0029] This embodiment mainly includes a microstrip primary feeder 1, a trapezoidal protruding bifurcation structure 2, metal bridge-shaped passages 3, 4, 5, 6, a shared dielectric beam (elastic dielectric membrane bridge) 7, a shared metal beam 8, independent downward metal beams 9, 10, metal piers 11, 12, 13, 14, 15, downward electrodes 16, 17, 18, 19, microstrip secondary feeders 20, 21, 22, 23, and voltage bias line groups 24, 25, 26, 27. By applying voltages to the voltage bias line groups 24, 25, 26, 27 respectively, a potential difference can be generated between the corresponding downward electrodes and the metal beams, thereby generating a downward electrostatic force to separately control the on / off of the four MEMS switch lines (the connection at both ends of the metal bridge-shaped passage); the four asymmetric MEMS switch structures are basically the same, and their positions are symmetrical about the axis of the microstrip primary feeder 1. One end of the switch is connected to the primary feeder, and the other end is connected to the secondary feeder. This switch structure is supported and combined through a shared composite beam to achieve overall miniaturization. The trapezoidal protruding bifurcation structure 2 consists of a T-junction power divider and two trapezoids, separating the four asymmetric MEMS switches in different spatial directions, reducing the loss of radio frequency performance while ensuring the placement space of the switch structure; the microstrip secondary feeders 21, 22 are first parallel to the microstrip primary feeder 1 and then deflected at a 45° angle to separate; the microstrip secondary feeders 20, 23 are perpendicular to the microstrip primary feeder 1.

[0030] The MEMS single-pole multi-throw switch has a unique electromechanical structure, including a shared dielectric beam 7 and a shared metal beam 8. The shared dielectric beam covers the four special-shaped MEMS switch structures, structurally supporting the metal beams at both ends of the structure respectively. The special-shaped MEMS structure is reflected in that one end of the fixed beam is a composite crane-shaped arm, and the other end is a dielectric material inclined folded arm. Both arms can be designed as shared structures, achieving overall miniaturization of the switch structure while making each switch not affect each other; in the case of sharing the metal beam, the two crane-shaped arms form a "day" character shape, and the voltage bias line groups can share the ground wire; the microstrip primary feeder, secondary feeder and voltage bias line groups of the switch together form a "rice" character configuration.

[0031] In the described single-pole four-throw switch, the four special-shaped MEMS switch structures are the same and are placed symmetrically along the primary feeder. Taking one of the switches as an example, each includes a metal pier 13, an elastic metal membrane bridge 8, an elastic dielectric membrane bridge 7, a pull-down electrode 18, a metal bridge-shaped path 5, and a voltage bias line 26. The elastic metal membrane bridge 8 and the pull-down electrode 18 largely overlap in the direction perpendicular to the substrate. The elastic dielectric membrane bridge 7 is an asymmetric structure and is mainly supported by the dielectric. Both the elastic metal membrane bridge 8 and the metal bridge-shaped path 5 are located below the elastic dielectric membrane bridge 7 and are tightly combined with the elastic dielectric membrane bridge 7. The elastic metal membrane bridge 8 and the metal bridge-shaped path 5 do not contact each other. The inclined folding arm made of dielectric material has a 45-degree corner at the end near the metal bridge-shaped path, making this end perpendicular to the long side of the bridge-shaped path.

[0032] The following is a more specific description:

[0033] Taking the Figure 1 partial structure of the switch shown in the appendix as an example, the key single-pole four-throw structure consists of a microstrip primary feeder 1, a trapezoidal protruding bifurcation structure 2, metal bridge-shaped paths 3, 4, 5, 6, a common dielectric beam (elastic dielectric membrane bridge) 7, a common metal beam 8, independent pull-down metal beams 9, 10, metal piers 11, 12, 13, 14, 15, pull-down electrodes 16, 17, 18, 19, microstrip secondary feeders 20, 21, 22, 23, and a voltage bias line group 24, 25, 26, 27.

[0034] Among them, the four special-shaped MEMS switches are placed symmetrically along the primary feeder; the common dielectric beam 7 covers all four special-shaped MEMS switch structures, which is an integrated design, and the dielectric beam and the metal beam are supported by each metal pier; each special-shaped MEMS switch is composed of a crane-shaped arm and an inclined folding arm. One end of the crane-shaped arm is a dielectric-metal hybrid beam, and one end of the folding arm is a single dielectric beam. The stress difference in the arm shape compensates for the abnormal deformation of the structure that may be caused by the pull-down electrode on one side; the metal bridge-shaped path is an independent metal structure on the dielectric beam 7, and there are metal contacts on the lower surface, which is responsible for signal transmission; the inclined folding arm made of dielectric material has a 45-degree corner at the end near the metal bridge-shaped path, making this end perpendicular to the long side of the bridge-shaped path; the inclined folding arm and its pier are shared by two special-shaped MEMS structures. In addition, the two special-shaped MEMS switches located on the axis of symmetry also share a dielectric-metal crane-shaped arm, which is supported by a metal pier 13, forming a stable "day" - shaped structure, which is convenient for realizing the miniaturization of the switch structure.

[0035] The pull-down structure of the MEMS switch is as shown in the appendix Figure 2As shown, taking one of the switch structures as an example, it is driven by a DC voltage, and there is a high-resistance wire at the positions of the metal pier 13 and the pull-down electrode 17 for applying a potential difference. When a voltage is applied to the voltage bias line group 25, a section of the elastic dielectric film bridge 7 made of silicon oxide or other dielectric materials is pulled down by the metal electrostatic force, and the contact points on the metal bridge-shaped path 4 connect the microstrip secondary feeder 21 and the trapezoidal protruding bifurcated structure 2, and this switch part is turned on; when the voltage is set to zero, the metal electrostatic force is released, and the dielectric film bridge 7 is restored by the elastic force, and the switch is turned off. When one of the four MEMS switch structures is turned on and the rest are turned off, this state is a working state, so this single-pole four-throw switch has a total of four working states, corresponding to the conduction of four terahertz signals respectively.

[0036] Figure 3 Describes a partial cross-sectional structure of the MEMS single-pole multi-throw switch. In terms of the constituent materials, the switch uses a high-frequency low-loss dielectric material as the substrate, such as a BT substrate, high-resistivity silicon, quartz, etc.; uses a corrosion-resistant low-resistivity metal material as the metal beam, such as copper, gold, etc.; uses a compound dielectric material with a low elastic coefficient as the dielectric beam, such as silicon oxide, etc. The metal beam is fabricated by the sacrificial layer technique, and the dielectric beam is tightly bonded to the metal beam, so that the dielectric structure can be driven by the downward force of the metal structure. To avoid short-circuit contact between the metal beam and the pull-down electrode after the metal beam is pulled down, a compound isolation layer is covered on the pull-down electrode. The stacked scheme proposed in this embodiment can obtain a stable MEMS switch structure with a low pull-down force.

[0037] The MEMS single-pole multi-throw switch board for performance testing is as shown in the appendix Figure 4 as follows

[0038] When a voltage is applied to both ends of the bias pads 28 and 29, the corresponding MEMS switch structure is turned on and the other three are turned off. The terahertz current will flow in from the microstrip primary feeder 1 and flow out from the microstrip secondary feeder 20; since there is no voltage difference on the other bias pads 30 - 34 at this time, the other microelectromechanical switch structures are turned off, and only a very weak current flows out from the three microstrip secondary feeders 21, 22, and 23 at this time. It can be directly seen from the figure that the four voltage bias line groups and the five microstrip feeders together form a "rice" character configuration, and this figure is axisymmetric about the extension direction of the microstrip primary feeder. Each primary feeder and secondary feeder are connected to the GSG probe pads 35 - 39 of a specific frequency band, and the microstrip line is converted into a grounded coplanar waveguide transmission line through a grounding via for the radio frequency performance test of the switch.

[0039] The distribution of the switch structure and the secondary feeder will both affect the switch performance, among which:

[0040] The internal structure size will have an important impact on the performance of the reconfigurable single-pole four-throw switch, and the specific manifestations are as follows:

[0041] a) The widths 43 and 44 of the metal path affect the impedance matching degree of the switch. Therefore, if the width 43 is too large or too small, the switching bandwidth will be too small or even the impedance will be mismatched.

[0042] b) The length of the metal path 44 affects the open-circuit isolation of the switch, and the slot length and the size of the radiating structure together determine the operating frequency band of the antenna;

[0043] c) The folded arm length of the dielectric beam is 46mm, which is used to adjust the pull-down voltage and switch response time in the pull-down state;

[0044] When constructing the switchboard, attach Figure 4 The displayed secondary feeder configuration has a significant impact on the performance of each switching state, specifically in the following ways:

[0045] d) The tilt angle of secondary feeder 20-23 affects the matching and loss level when the switch is switched to this path;

[0046] e) The spacing between the secondary feed lines 21 and 22, as well as the final direction of the secondary feed lines, will significantly affect the antenna port matching and operating bandwidth;

[0047] f) The length 40 and width 41 of the trapezoidal protruding bifurcation structure directly affect the RF performance of the high-frequency single-pole multi-throw switch. If the value is too large or too small, it will lead to a decrease in the consistency of the performance of each switching state of the switch, or an overall decrease in performance.

[0048] With attachment Figure 2 , 4 A typical single-pole four-throw switch, for example, consists of a switch structure, bias pads 28-34, and GSG probe pads 35-39. The size of the GSG probe pads limits the routing and distribution of the secondary microstrip feed line, and their matching bandwidth ultimately limits the operating frequency band of the switch under test. A well-designed probe pad can affect the switch's test performance but not its practical application performance. In practical system applications, reducing the length of the secondary microstrip feed line can further improve its RF performance.

[0049] Therefore, selecting a reasonable fan-out configuration and a two-stage microstrip feeder is of great significance for improving the performance of terahertz single-pole multi-throw switches. The final structural parameters of the switch are the result of comprehensive optimization.

[0050] This small terahertz MEMS single-pole four-throw switch based on a shared composite beam is illustrated here using an example of a size combination (the following data are in micrometers):

[0051] when Figure 1 The dimensions of the structure are:

[0052] Structure 40 = 30, structure 41 = 30, structure 42 = 45;

[0053] when Figure 2 The dimensions of the structure are:

[0054] Structure 43 = 7, structure 44 = 25, structure 45 = 41, structure 46 = 28;

[0055] when Figure 3 The dimensions of the structure are:

[0056] Structure 47 = 1710, Structure 48 = 2100;

[0057] The total thickness of the high-frequency, low-loss dielectric substrate is 50, the height difference between the switch metal bridge-shaped path 4 and the substrate is 1.8, and the metal layer thickness of the microstrip line and the metal ground is 1.

[0058] The simulation diagram of the reflection coefficient of the terahertz MEMS single-pole four-throw switch based on the shared composite beam is as follows:

[0059] Figure 5 The figure shows the port S-parameter curves of the terahertz MEMS single-pole four-throw switch based on a shared composite beam when switch path 4 is conducting. Switch path 4 corresponds to GSG probe pad 37. The results show the transmission loss, port reflection, and isolation of the switch in the frequency range of 200-350 GHz. Above 205 GHz, S(35,35) is less than -15 dB, meaning the return loss at input pad 35 is greater than 15 dB; below 340 GHz, S(37,35) is greater than -2 dB, meaning the transmission loss at the input and output ends is less than 2 dB; the other three curves represent the input and output isolation at the non-conducting port, all of which are greater than 15 dB.

[0060] Figure 6 The figure shows the port S-parameter curves of the terahertz MEMS single-pole four-throw switch based on a shared composite beam when switch path 3 is conducting. Switch path 3 corresponds to GSG probe pad 36. At frequencies below 300 GHz, S(35,35) is less than -15 dB, meaning the return loss at input pad 35 is greater than 15 dB; S(36,35) is greater than -2.4 dB at frequencies below 300 GHz, meaning the transmission loss at the input and output ends is less than 2.4 dB; the other three curves represent the input and output isolation at the non-conducting port, all of which are above 15 dB.

[0061] As can be seen, a miniaturized terahertz MEMS single-pole quad-throw switch can achieve RF channel switching in the 205-300 GHz terahertz band. The above results are affected by the bandwidth of the GSG probe pad. The actual switch structure has a return loss greater than 15 dB, an in-band insertion loss less than 1.8 dB, and an isolation greater than 15 dB in the DC-350 GHz band.

[0062] The above is just one example. To obtain MEMS single-pole four-throw switches under different operating frequency bands, different parameters can be adjusted according to the specific implementation method. For example, the operating frequency can be adjusted by adjusting the length and width of the metal path, the tilt angle of the secondary feed line, and the spacing of the secondary feed line, as well as adjusting the transmission loss and impedance matching. The switch can also be implemented through other MEMS processes.

Claims

1. A small terahertz MEMS single-pole four-throw switch based on a shared composite beam, characterized in that, It includes a microstrip primary feed line (1), a trapezoidal protruding bifurcation structure (2), a voltage bias line group, an irregularly shaped MEMS switch, and a microstrip secondary feed line (20, 21, 22, 23). The trapezoidal protruding bifurcation structure (2) consists of a T-shaped power divider and two trapezoidal components, wherein the two trapezoidal components correspond one-to-one with the two ends of the T-shaped power divider; the lower bottom edge of the trapezoidal component is close to one side of the end of the T-shaped power divider, and the two trapezoidal components are located at the two output ends of the T-shaped power divider in the same direction. The output end of the microstrip primary feed line is connected to the input end of the T-junction power divider; the end of the T-junction power divider and the upper bottom edge of the trapezoidal component are connected to the microstrip secondary feed line one by one through irregularly shaped MEMS switches, and the irregularly shaped MEMS switches correspond one-to-one with the microstrip secondary feed line. Four irregularly shaped MEMS switches share the same elastic dielectric membrane bridge (7). The metal bridge-shaped path and pull-down metal beam on each irregularly shaped MEMS switch are located on the lower surface of the elastic dielectric membrane bridge. The elastic dielectric membrane bridge and pull-down metal beam are supported and suspended by corresponding metal bridge piers, and a pull-down electrode is provided below the pull-down metal beam. The voltage bias line group is connected to the corresponding pull-down electrode and metal bridge pier. The two ends of the metal bridge-shaped path are respectively used to connect the microstrip primary feed line and the microstrip secondary feed line. The metal bridge-like path and the pull-down metal beam on the same irregularly shaped MEMS switch are adjacent but not in contact. Two irregularly shaped MEMS switches corresponding to the bottom edge of the trapezoidal component share a pull-down metal bridge, which has a H-shaped structure. The pull-down metal bridges of the two irregularly shaped MEMS switches corresponding to the output terminals of the T-junction power divider are both U-shaped structures.

2. The miniature terahertz MEMS single-pole four-throw switch based on a shared composite beam according to claim 1, characterized in that, The initial segment of the microstrip secondary feed line connected by the trapezoidal component is parallel to the microstrip primary feed line, and the microstrip secondary feed line connected to the end of the T-junction power divider is perpendicular to the microstrip primary feed line. Among them, the two microstrip secondary feed lines connected by trapezoidal components are both bent at 135° and set opposite each other.

3. The miniature terahertz MEMS single-pole four-throw switch based on a shared composite beam according to claim 1, characterized in that, The elastic dielectric membrane bridge portion above the metal bridge-shaped passage is perpendicular to the long side of the metal bridge-shaped passage.

4. The miniature terahertz MEMS single-pole four-throw switch based on a shared composite beam according to claim 1, characterized in that, A high-frequency, low-loss dielectric material is used as the substrate; a corrosion-resistant, low-resistivity metal material is used as the metal beam; a compound dielectric material with a low elastic coefficient is used as the dielectric membrane bridge; the metal beam is fabricated using a sacrificial layer technique, and the dielectric membrane bridge is tightly bonded to the metal beam, allowing the dielectric membrane bridge to be driven by the downward pull of the metal beam.

5. The miniature terahertz MEMS single-pole four-throw switch based on a shared composite beam according to claim 1, characterized in that, The microstrip primary feed line, the microstrip secondary feed line, and the voltage bias line group together form a star-shaped configuration.

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