Terahertz frequency band low-loss high-isolation MEMS switch

Abstract

The invention belongs to a terahertz-band low-loss high-isolation MEMS switch, and belongs to the field of radio frequency front-end devices. The switch bridge pier structure is composed of a metal beam, an upper electrode through hole group, a trapezoidal connector, a contact, a silicon nitride capacitor insulating layer, a lower electrode, a silicon nitride electrode insulating layer, a coplanar waveguide microwave transmission line structure, a direct current bias high-resistance line, a gold wire, a gold PAD bonding pad patch, a dielectric substrate, a backboard metal ground, a grounding metal cylinder and a metal bridge. When feeding is carried out through the coplanar waveguide, the radio frequency characteristics of the switch in the on and off states are analyzed. When the switch is switched off, the isolation degree can reach-24.94 dB, and the low-insertion-loss high-isolation terahertz filter has the characteristics of low insertion loss and high isolation degree at high frequency, can be widely applied to the terahertz communication field, and can be applied to radio frequency devices such as microwave circuits and antennas. The switch adopts a single-layer metal beam design, is simple in structure and convenient to manufacture, and can be quickly etched and manufactured.

Description

Technical Field

[0001] The present invention relates to a terahertz frequency band low-loss and high-isolation MEMS switch, which is mainly used in micro-electromechanical systems and terahertz communication systems and belongs to the field of radio frequency front-end devices. Background Art

[0002] MEMS switches are miniature mechanical switches that are usually driven by voltage. Their main applications include wireless communications, radio frequency (RF) systems, sensors, and microwave circuits. Compared with traditional semiconductor switches, MEMS switches have lower insertion loss, higher isolation, and lower power consumption, so they are very popular in terahertz communication applications.

[0003] The basic principle of metal capacitive MEMS switch is to apply a DC bias voltage to the electrode. The metal beam above the electrode will deform and bend under the action of electrostatic force, and the contact above the signal line will also be pulled down synchronously, thereby changing the distance between the metal contact and the signal line. The capacitance in between changes, thereby hindering the transmission of microwave signals until it is shut down.

[0004] The main advantages of metal capacitive MEMS switches are: 1. Low power consumption: The energy consumption of capacitive MEMS switches is mainly concentrated during the switching action, and there is almost no power consumption in the stable state. 2. High isolation: Because the mechanical movement isolates the electrical connection between the electrodes, MEMS switches can provide high isolation and reduce signal leakage in high-frequency applications. 3. Low insertion loss: Compared with traditional semiconductor switches (such as PIN diodes and FET switches), MEMS switches have lower insertion loss at high frequencies, which helps to improve the overall efficiency of the system. 4. Small size and light weight: MEMS technology allows complex mechanical structures to be miniaturized, making the switch much smaller in size and weight than traditional mechanical switches, suitable for integration into compact devices and systems, and widely used in micro-electromechanical systems.

[0005] Although capacitive MEMS switches have advantages in many aspects, they still face some technical challenges in practical applications, including: 1 Reliability: The mechanical structure may wear, adhere, and other phenomena during repeated operations, resulting in a limited service life of the switch. 2 Breakdown voltage: Due to the miniaturization of the structure, the distance between the electrodes is very small, which increases the risk of dielectric breakdown under high voltage. 3 Manufacturing complexity: The manufacturing precision requirements are high and the process is complex, which increases the production cost and difficulty. 4 Response speed: Although the response speed of the MEMS switch is relatively fast, it is still slightly slower than that of a purely electrically controlled switch.

[0006] The main applications of capacitive MEMS switches include the following areas:

[0007] RF communication: used to switch RF signal paths and improve signal transmission quality in communication systems.

[0008] Microwave circuit: used in high-frequency equipment such as radar and satellite communications, with the advantages of low loss and high isolation.

[0009] Tunable filters: MEMS switches can be used to implement frequency-tunable filters to adapt to signal processing in different frequency bands.

[0010] Sensor and antenna arrays: Flexible system configuration and functionality enhancements can be achieved by switching different sensor elements or antenna units. Summary of the invention

[0011] In order to solve the problems existing in the background technology, the present invention designs a low-loss and high-isolation MEMS switch in the terahertz frequency band, which can meet the design of low-loss and high-isolation RF switches in the millimeter-wave terahertz frequency band and can be applied to microwave circuits, reconfigurable antennas and other fields.

[0012] The designed switch has a low profile, with a single-layer quartz glass dielectric plate as the substrate, and metal bridge piers, electrodes and metal beams etched on the surface. It has a simple structure, low process difficulty, and is easy to process and test. The designed switch has a moderate driving voltage, which solves the problems of too high voltage being difficult to pull down and too low voltage being easy to pull in and collapse. After impedance matching, it is installed on a coplanar waveguide microstrip transmission line. After simulation, its RF characteristics are good, the isolation is high when the switch is disconnected, the insertion loss is small when it is turned on, the mechanical strength is high, and the reliability is good.

[0013] In order to solve the above technical problems, the present invention is achieved through the following technical solutions:

[0014] A low-loss and high-isolation MEMS switch in the terahertz frequency band, comprising a metal bridge pier, a metal beam, a gold PAD pad patch, a contact and an electrode;

[0015] The contact point is located above the fracture of the transmission line structure; two metal bridge piers are provided, which are respectively located on both sides of the transmission line structure; the metal beams correspond to the metal bridge piers one by one, and one end of the metal beam is connected to the top of the corresponding metal bridge pier; both ends of the contact point are connected to the metal beam on the same side through a trapezoidal connector;

[0016] The electrodes correspond to the metal beams one by one, the electrodes are located directly below the corresponding metal beams, and a silicon nitride electrode insulating layer is provided on the upper surface of the electrodes; a silicon nitride capacitor insulating layer is provided on the lower surface of the contacts;

[0017] The gold PAD pad patches are provided with two, two electrodes are connected to one of the gold PAD pad patches, and two metal bridge piers are connected to the other gold PAD pad patch.

[0018] Furthermore, the electrodes and metal bridge piers are connected to corresponding gold PAD pads through DC bias lines.

[0019] Furthermore, the DC bias line may be made of gold wire.

[0020] Furthermore, the transmission line structure is located on the upper surface of the dielectric substrate, and a backplane metal ground is provided on the lower surface of the dielectric substrate; the metal bridge piers, electrodes, and metal beams are all etched on the upper surface of the dielectric substrate, and the dielectric substrate is a single-layer quartz glass medium;

[0021] The transmission line structure grounding metallization through hole is connected to the backplane metal ground.

[0022] Furthermore, the metal beam includes an upper electrode and four arms, the four arms are respectively two arc-shaped curved arms and two straight arms; the two straight arms are directly connected to the metal bridge pier and are parallel to each other, and the two arc-shaped curved arms are respectively connected to opposite sides of the metal bridge pier;

[0023] The other ends of the straight arm and the arc-shaped curved arm are connected to the same side of the upper electrode; the arc-shaped curved arm gradually narrows from the metal bridge pier end to the upper electrode end; and there are gaps between adjacent arms.

[0024] Furthermore, the upper electrode is provided with a plurality of through holes.

[0025] Compared with the background technology, the present invention has the following advantages:

[0026] a) Low insertion loss when on and high isolation when off. Compared with active switching devices such as PIN diodes, the insertion loss in the terahertz band is small in the on state, and S21 is greater than -0.21dB. The matching can work at low frequencies to 168GHz, with a significant working frequency of 140GHz. When turned off, the isolation is higher than that of ohmic contact MEMS switches or active electronically controlled switches, and S21 is less than -25dB.

[0027] b) The pull-in voltage is moderate and the reliability is high. After software modeling and simulation, the pull-in voltage is about 22.73V and the pull-in distance is 0.7um. This voltage is moderate, avoiding problems such as too high voltage being difficult to pull down and too low voltage pull-in collapse. The switch has high reliability and stability.

[0028] c) The structure is simple and easy to manufacture. Metal piers, metal beams and coplanar waveguide microstrip lines are etched on the quartz glass substrate, and metalized vias are opened in the dielectric as the grounded coplanar waveguide. Single-layer board processing is easier to achieve. The coplanar waveguide microstrip transmission line structure is designed to verify the excellent RF transmission characteristics of the MEMS switch. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a top view schematic diagram of a low-loss and high-isolation MEMS switch in the terahertz frequency band;

[0030] Figure 2yes Figure 1 A front view of the structure;

[0031] Figure 3 It is a graph showing the relationship between the bias voltage and pull-down displacement of the MEMS switch;

[0032] Figure 4 This is the impedance matching S11 and insertion loss S21 curve when the MEMS switch is turned on;

[0033] Figure 5 This is the isolation S21 curve when the MEMS switch is turned off; DETAILED DESCRIPTION

[0034] The following is combined with Figure 1-5 The specific implementation modes of the present invention are further described in detail with reference to the accompanying drawings and examples.

[0035] A terahertz band low-loss high-isolation MEMS switch comprises a bridge pier structure 1, 2, metal beams 3, 4, upper electrode through-hole groups 5, 6, trapezoidal connections 7, 8, contacts 9, a silicon nitride capacitor insulating layer 10, lower electrodes 11, 12, and silicon nitride electrode insulating layers 13, 14. The switch is characterized in that it also comprises a coplanar waveguide microwave transmission line structure 15, a DC bias high-resistance line 16, a gold wire 17, a gold PAD solder pad patch 18, a dielectric substrate 19, a backplane metal ground 20, a grounded metal cylinder 21, and a metal bridge 22.

[0036] The MEMS switch and electrode have symmetrical structures on the left and right sides, the same size, and a capacitive fixed beam MEMS switch composed of a single layer of metal. The coplanar waveguide microwave transmission line has symmetrical structures on the left and right sides, the same size, the same radius of the grounding metallized through-holes, the same arrangement spacing, and symmetrical positions. The metal bridges have the same height and are symmetrically positioned on the left and right sides. The feeding network is designed with impedance matching, and the coplanar waveguide feeding port 23 can be probe-fed by a radio frequency probe.

[0037] Attach Figure 1 Taking the terahertz frequency band low-loss high-isolation MEMS switch as an example, it is composed of pier structures 1, 2, metal beams 3, 4, upper electrode through-hole groups 5, 6, trapezoidal connections 7, 8, contacts 9, silicon nitride capacitor insulating layer 10, lower electrodes 11, 12, and silicon nitride electrode insulating layers 13, 14.

[0038] The coplanar waveguide microwave transmission line adopts metallized via grounding to optimize its impedance matching characteristics. In order to reduce the loss, the metal materials of all structures are metals with low resistivity, such as aluminum, copper, gold, etc., and the dielectric substrate 19 is made of materials with low loss, such as high-resistance silicon, Rogers5880, etc. In this example, the metal material is gold, the dielectric substrate is quartz glass, the dielectric constant is 3.78, and the loss tangent is 0.0008.

[0039] The gold PAD patch pad is connected to the external PCB test substrate through the gold wire bonding process, and the PCB board can provide it with voltage and ground potential. The bridge piers on both sides of the switch are grounded through high-resistance bias lines, and the electrodes are connected to the bias voltage. When the bias voltage gradually increases, the electrostatic force generated by the electrode will attract the electrode on the metal beam to deform and bend downward, driving the contact above the signal line to produce a downward displacement. After modeling and simulation with cmosol software, a curve diagram of the relationship between bias voltage and downward displacement can be obtained. See the attached figure. Figure 3 After the contact is pulled down a certain distance, the capacitance between the bridge and the line above the signal line changes, which will gradually reflect the transmission of the signal. When the voltage reaches the critical value of the pull-in voltage, the contact is connected to the signal line through the insulating film, and the capacitance is equivalent to the capacitance between the signal line and the ground. When the distance between the signal line and the metal beam decreases, the capacitance increases. At this time, most of the energy is coupled by the metal beam and introduced into the grounding point. The signal is isolated and cannot be transmitted to another port through the transmission line. The switch has a high degree of isolation.

[0040] Gradually reduce the bias voltage of the lower electrode, the electrostatic force gradually decreases, due to the isolation of the insulating layer between the signal line and the contact and the insulating layer between the upper and lower electrodes, the contact and the signal line can be quickly separated, the metal beam gradually rebounds, the distance between the contact and the signal line increases, the capacitance decreases, the signal is difficult to couple from the metal beam to the ground, most of the energy is transmitted to the other port through the transmission line, there is no need to lift it to a very high height, only need to restore to the state before pulling down to ensure a low insertion loss.

[0041] Among them, silicon nitride, as the dielectric layer of the capacitor, can not only prevent the problem of direct metal contact being unable to disconnect and rebound, but also use its higher dielectric constant to improve the coupling capacitance of the electrode in the on state.

[0042] Usually, MEMS switches can achieve an isolation higher than 20dB and an insertion loss lower than 0.2dB only when the operating frequency is below 1GHz. This design has been rigorously modeled to ensure its excellent mechanical and RF performance, and can still have a high isolation of 20dB and a low insertion loss of 0.2dB at a high frequency of 140GHz. The metal beam piers are not directly erected on the metal ground on both sides of the coplanar waveguide, but are connected to the ground PAD through a high-resistance bias line. This measure is to isolate the DC bias and RF signals to avoid burning the coplanar waveguide.

[0043] From the perspective of material mechanics, the switch effectively releases residual stress by opening holes in the metal beam. The elastic coefficient of the switch is adjusted through the combined design of arc-shaped curved arms and straight-connected arms to ensure that the pull-down voltage is within a reasonable range of 20V-30V. The symmetrical structure of the fixed beam ensures the stability of the processing technology and the reliability of the switch, and fatigue testing can be carried out.

[0044] The structure of the low-loss and high-isolation MEMS switch in the terahertz frequency band is described in an example using a size combination (the following data is in micrometers):

[0045] when Figure 1 The dimensions of the structure are:

[0046] The bridge pier structures 1 and 2 have a length × width of 25 × 10, the metal beams 3 and 4 have a length × width of 35 × 20, the upper electrode through hole groups 5 and 6 have a diameter of 6, the trapezoidal connections 7 and 8 have a long side / short side × width of 35 / 20.6 × 11, the contact 9 has a length × width of 28 × 20.6, the coplanar waveguide microwave transmission line structure 15 has a length × width of 445 × 70, the DC bias high resistance line 16 has a width of 5 um, the gold PAD pad patch 18 has a size of 100 × 100, the dielectric substrate 19 has a size of 700 × 700, and the grounding metal cylinder 21 has a diameter of 50;

[0047] when Figure 2 The dimensions of the structure are:

[0048] The height of the silicon nitride capacitor insulating layer 10 is 0.1, the length×width×height of the lower electrodes 11 and 12 is 35×20×1, the height of the silicon nitride electrode insulating layers 13 and 14 is 0.1, the height of the dielectric substrate 19 is 100, and the height of the structure 20 is 1;

[0049] When the coplanar waveguide is fed, the center frequency is solved to be 140 GHz, which belongs to the millimeter wave D band.

[0050] At this time, the relationship curve between the pull-down displacement and driving voltage of the low-loss and high-isolation MEMS switch contact in the terahertz frequency band is as follows:

[0051] Figure 3 The curve showing the relationship between the contact pull-down displacement and the driving voltage of the switch shows that when the driving voltage is 22.7V, the pull-down displacement is 1.2um. At this time, the switch is closed, and 22.7V is the closing voltage.

[0052] At this time, the S21 isolation curve simulation diagram of the switch is:

[0053] Figure 5 It is shown in the figure that when the center frequency of the switch is 140GHz, the S21 reaches -24.94dB, and the switch has a high isolation.

[0054] The bias voltage is 0 and the contact is not pulled down. At this time, the switch is in the on state:

[0055] Figure 4Shown in the figure are the reflection coefficient S11 curve and insertion loss S21 curve when the switch is in the on state, which shows that the S11 of the switch is significantly less than -10dB when operating in the frequency range of 50GHz-168.5GHz. When the switch is on, the insertion loss is less than 0.21dB, and the loss is very small.

[0056] It can be seen that the switch has a wide operating bandwidth and very low insertion loss when it is turned on in the D-band, and has a high isolation when it is turned off. The structure design is simple, consisting of only a single-layer board, with a low profile, and is easy to process and realize.

[0057] The above is only an example. If one wants to obtain a low-loss and high-isolation MEMS switch in the terahertz band at different operating frequencies and different driving voltages, different parameters can be adjusted according to the specific implementation method.

Claims

1. A low-loss and high-isolation MEMS switch in the terahertz frequency band, characterized in that: Including metal piers, metal beams, gold PAD pads, contacts and electrodes; The contact point is located above the fracture of the transmission line structure; two metal bridge piers are provided, which are respectively located on both sides of the transmission line structure; the metal beams correspond to the metal bridge piers one by one, and one end of the metal beam is connected to the top of the corresponding metal bridge pier; both ends of the contact point are connected to the metal beam on the same side through a trapezoidal connector; The electrodes correspond to the metal beams one by one, the electrodes are located directly below the corresponding metal beams, and a silicon nitride electrode insulating layer is provided on the upper surface of the electrodes; a silicon nitride capacitor insulating layer is provided on the lower surface of the contacts; The gold PAD pad patches are provided with two, two electrodes are connected to one of the gold PAD pad patches, and two metal bridge piers are connected to the other gold PAD pad patch.

2. The terahertz band low-loss and high-isolation MEMS switch according to claim 1, characterized in that: The electrodes and metal bridge piers are connected to corresponding gold PAD pads through direct current bias lines.

3. The terahertz band low-loss and high-isolation MEMS switch according to claim 2, characterized in that: The DC bias line may be made of gold wire.

4. The terahertz band low-loss and high-isolation MEMS switch according to claim 1, characterized in that: The transmission line structure is located on the upper surface of the dielectric substrate, and a backplane metal ground is provided on the lower surface of the dielectric substrate; the metal bridge piers, electrodes, and metal beams are all etched on the upper surface of the dielectric substrate, and the dielectric substrate is a single-layer quartz glass medium; The transmission line structure grounding metallization through hole is connected to the backplane metal ground.

5. The terahertz band low-loss and high-isolation MEMS switch according to claim 1, characterized in that: The metal beam comprises an upper electrode and four arms, wherein the four arms are respectively two arc-shaped curved arms and two straight arms; the two straight arms are directly connected to the metal bridge pier and are parallel to each other, and the two arc-shaped curved arms are respectively connected to two opposite sides of the metal bridge pier; The other ends of the straight arm and the arc-shaped curved arm are connected to the same side of the upper electrode; the arc-shaped curved arm gradually narrows from the metal bridge pier end to the upper electrode end; and there are gaps between adjacent arms.

6. The terahertz band low-loss and high-isolation MEMS switch according to claim 5, characterized in that: The upper electrode is provided with a plurality of through holes.

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