Droplet RF MEMS switch based on piezoelectric ceramic film actuation

Abstract

The invention discloses a droplet radio frequency micro-electromechanical system switch based on piezoelectric ceramic film drive, which mainly solves the problems of large driving voltage and weak resistance to external acceleration signal interference of existing radio frequency micro-electromechanical system switches. The switch comprises three layers of substrates, namely, lower, middle and upper layers. The upper substrate (3) is provided with two metal pads (9, 10), and the upper and lower surfaces are provided with piezoelectric ceramic films (6) and back cavities (7) respectively; the lower substrate (1) is provided with a coplanar waveguide (4) composed of two ground electrodes (41, 43) and two signal electrodes (42, 44); the middle substrate (2) is provided with a through groove (8), which is located above the signal electrode, and part of the two ground electrodes is exposed in the through groove; the through groove is aligned with the center of the back cavity, and is connected from top to bottom, and contains a mercury droplet (5); the three layers of substrates are packaged as one. The invention has low driving voltage, strong resistance to external acceleration signal interference, small size, low cost, and can be used in micro-electromechanical systems.

Description

Technical Field

[0001] The present invention belongs to the field of electromechanical technology, and in particular relates to a liquid drop radio frequency switch which can be used in a micro-electromechanical system. Background Art

[0002] Radio frequency micro-electromechanical system (RF MEMS) devices have attracted great attention internationally due to their advantages such as small size, light weight and mass production. RF MEMS switches are basic components of RF MEMS devices such as RF MEMS phase shifters, filters, and reconfigurable antennas. At the same time, RF MEMS switches are an important part of core devices in the fields of autonomous driving, the Internet of Things, and 5G chips. Therefore, it can be predicted that RF MEMS technology will usher in large-scale development in the near future. At present, RF MEMS switches use mechanical cantilever beams as movable parts, and electrostatic force drives the beams to move up and down to achieve the purpose of turning on the switch. However, since the switch needs to work in a high-frequency environment, the reliability of RF MEMS switches is reduced or failure is more serious. The main problems come from two aspects. One is the failure of the switch's working adhesion, and the other is the degradation of the switch's electrical performance due to the increase in the switch's contact resistance.

[0003] In order to solve the failure problem of traditional RF MEMS switches, researchers have proposed using metal droplets instead of cantilever beams, and through the principle of electrowetting on the dielectric, drive the movement of droplets in the plane to achieve the "open" and "close" actions of the switch. For example, in 2009, Chang-Jin Kim of the University of California, Los Angeles published an article in the Journal of Microelectromechanical Systems, proposing a droplet RF MEMS switch based on the principle of electrowetting on the dielectric. The driving voltage of the switch needs to reach 100V, and the switch uses 4 micro frames to control the movement of droplets in the plane. This droplet-type RF MEMS switch requires a driving voltage greater than 100V, and the micro frame cannot limit the deformation of the droplet, and the ability to resist interference from external acceleration signals is weak. At the same time, the droplet needs to roll a long distance in the microchannel inside the switch, resulting in a larger switch volume. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and propose a droplet RF MEMS switch and a manufacturing method based on piezoelectric ceramic film drive, which utilizes piezoelectric ceramic film to drive the movement of droplets and reduce the driving voltage of the switch; limits the movement of droplets through double-stage microfluidics to increase the ability of the RF MEMS switch to resist interference from external acceleration signals; and combines MEMS technology to reduce the size and cost of the switch.

[0005] In order to achieve the above-mentioned object, the present invention is based on a droplet radio frequency micro-electromechanical system switch driven by a piezoelectric ceramic film, comprising a lower substrate 1, an intermediate substrate 2 and an upper substrate 3, wherein the upper substrate 3 is provided with two metal pads 9, 10, and the lower substrate 1 is provided with a coplanar waveguide 4, wherein the coplanar waveguide 4 comprises two ground electrodes 41, 43 and two signal electrodes 42, 44, and is characterized in that:

[0006] The upper and lower surfaces of the upper substrate 3 are provided with a piezoelectric ceramic film 6 and a back cavity 7, respectively.

[0007] The intermediate substrate 2 is provided with a through groove 8, which is located above the two signal electrodes 42, 44, and parts of the two ground electrodes 41, 43 are exposed in the through groove 8.

[0008] The through groove 8 is aligned with the center of the back cavity 7 and is connected vertically, and contains a mercury droplet 5.

[0009] The lower substrate 1, the middle substrate 2 and the upper substrate 3 are packaged as one;

[0010] Furthermore, a lower driving electrode 61 and an upper driving electrode 62 are deposited on the upper and lower surfaces of the piezoelectric ceramic film 6, respectively. The lower driving electrode 61 is connected to the first metal pad 9, and the upper driving electrode 62 is connected to the second metal pad 10.

[0011] Furthermore, the plane size of the intermediate substrate 2 is smaller than the plane size of the lower substrate 1 and is located in the middle of the lower substrate 1;

[0012] Furthermore, the plane size of the upper substrate 3 is the same as the plane size of the intermediate substrate 2, and the upper substrate 3 and the intermediate substrate 2 are aligned on all sides during packaging;

[0013] Furthermore, the first signal electrode 42 and the second signal electrode 44 are located between the first ground electrode 41 and the second ground electrode 43 and are at the same distance from the two ground electrodes;

[0014] Furthermore, the mercury droplet 5 in the back cavity enters the through groove 8 in a small amount when the switch is closed, and enters the through groove 8 in a large amount when the switch is turned on, and contacts the first signal electrode 42 and the second signal electrode 44 .

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. The present invention uses a piezoelectric ceramic film to drive the movement of mercury droplets, and uses a two-stage microchannel composed of a back cavity and a through groove to reduce the distance that the mercury droplets move during the switch action, thereby reducing the driving voltage of the switch.

[0017] 2. The present invention utilizes the liquid-solid contact mode between the mercury droplet and the two signal electrodes, thereby improving the reliability of the switch and reducing the contact resistance of the switch.

[0018] 3. Since the present invention uses mercury droplets, it can quickly regroup from a dispersed state under a large impact. At the same time, the two-stage microchannel composed of the back cavity and the through groove limits the movement and deformation of the mercury droplets, thereby improving the impact resistance of the switch. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0020] Figure 2 It is a schematic diagram of the structure of the upper substrate in the present invention;

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

[0022] Figure 4 is a schematic diagram of the present invention in the "off" state;

[0023] Figure 5 It is a schematic diagram of the present invention in the "on" state. DETAILED DESCRIPTION

[0024] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0025] Reference Figure 1 This example includes a lower substrate 1, an intermediate substrate 2 and an upper substrate 3, wherein the upper substrate 3 is provided with a piezoelectric ceramic film 6 and two metal pads 9 and 10, the lower substrate 1 is provided with a coplanar waveguide 4, the intermediate substrate 2 adopts SU-8 photoresist material with a thickness of 100μm to 150μm, is provided with a through groove 8, and the through groove 8 is filled with mercury droplets 5, the lower substrate 1 and the intermediate substrate 2 are packaged by MEMS process, the intermediate substrate 2 and the upper substrate 3 are packaged by ultraviolet adhesive, the plane size of the intermediate substrate 2 is smaller than the plane size of the lower substrate 1, and is located in the middle position of the lower substrate 1, the plane size of the upper substrate 3 is the same as the plane size of the intermediate substrate 2, and the upper substrate 3 and the intermediate substrate 2 are aligned on all sides during packaging.

[0026] Reference Figure 2 The upper substrate 3 described in this example is made of single crystal silicon material with a thickness of 450μm to 500μm, and a piezoelectric ceramic film 6 and a back cavity 7 are provided on its upper and lower surfaces respectively. A lower driving electrode 61 and an upper driving electrode 62 are deposited on the upper and lower surfaces of the piezoelectric ceramic film 6 respectively. The lower driving electrode 61 and the upper driving electrode 62 are connected to the first metal pad 9 and the second metal pad 10 respectively.

[0027] The preparation process of the upper substrate 3 and the structures thereon is as follows:

[0028] A 200nm-300nm thick layer of silicon dioxide is first deposited on the upper and lower surfaces of the upper substrate 3 by plasma enhanced chemical vapor deposition (PECVD) process, and then a 30nm-50nm thick layer of titanium metal and a 200nm-250nm thick layer of platinum metal are sputtered on the upper surface of the silicon substrate after the silicon dioxide deposition by a magnetron sputtering apparatus to form a lower driving electrode 61;

[0029] Spin-coat a piezoelectric ceramic PZT sol on a platinum-plated surface to prepare a PZT film with a thickness of 1 μm to 1.5 μm, spin-coat a positive photoresist BP212 on the crystallized PZT film, and bake it on a hot plate at 85° C. for 30 minutes to harden the film, then use a photolithography machine to align and expose, place the exposed sample in a 0.5% NaOH solution for development, and bake it at 85° C. for 30 minutes after the development is completed, sputter a titanium / platinum electrode layer with a thickness of 150 nm to 200 nm on the sample, soak the sputtered sample in an acetone solution, and peel off the titanium / platinum metal on the photoresist mask to obtain a patterned upper driving electrode 62;

[0030] The same photolithography process is used to spin-coat photoresist on the patterned platinum electrode layer, and a PZT masking layer is obtained after exposure and development. The sample is placed in a PZT etching solution to etch the film to obtain a piezoelectric ceramic film 6 structure;

[0031] First, a photoresist pattern of two pads 9 and 10 is prepared on the surface of the upper substrate by using a photolithography process, and then a magnetron sputtering device is used to deposit 150nm to 200nm thick gold on the upper surface of the upper substrate to obtain two pads 9 and 10;

[0032] First, a photoresist masking layer of the back cavity 8 is made on the back side of the upper substrate 3 by using a photolithography process, and then the silicon substrate is etched by using a dry etching process DRIE to finally obtain the back cavity 8.

[0033] Reference Figure 3 The lower substrate 1 described in this example is made of glass material with a thickness of 300μm to 500μm, and a coplanar waveguide 4 is provided on its upper surface. The coplanar waveguide 4 includes two ground electrodes 41 and 43, namely a first ground electrode 41 and a second ground electrode 43, and two signal electrodes 42 and 44, namely a first signal electrode 42 and a second signal electrode 44. The two signal electrodes 42 and 44 are located between the first ground electrode 41 and the second ground electrode 43, and are at the same distance from the two ground electrodes.

[0034] The preparation process of the lower substrate 1 and the structures thereon is as follows:

[0035] A photoresist pattern of a first ground electrode 41, a second ground electrode 43, a first signal electrode 42, and a second signal electrode 44 is first prepared on the upper surface of the lower substrate 1 by using a photolithography process, and then a layer of nickel / chromium metal film is deposited on the surface of the photoresist pattern by a magnetron sputtering process, and the photoresist pattern is immersed in an acetone solution so that the metal deposited on the photoresist is washed away by the acetone solution, and the metal directly covering the surface of the lower substrate 1 is retained, thereby obtaining a coplanar waveguide 4 composed of the two ground electrodes 41, 43 and the two signal electrodes 42, 44.

[0036] The mercury droplet 5 has a surface tension of 0.485 N / m at room temperature and has a large surface tension. When no voltage is applied, the distance between the mercury droplet 5 and the coplanar waveguide 4 is large; when voltage is applied, the piezoelectric ceramic 6 is deformed, causing the mercury droplet 5 to contact the first signal electrode 42 and the second signal electrode 44, thereby realizing the "on" action of the switch; when the voltage is stopped, the mercury droplet 5 will return to its initial position due to the effect of surface tension, thereby realizing the "on" and "off" working states of the present invention.

[0037] Reference Figure 4 When the switch is in the off state, the potential between the lower driving electrode 61 and the upper driving electrode 62 is zero, the piezoelectric ceramic 6 does not deform, the mercury droplet 5 does not contact the first signal electrode 42 and the second signal electrode 44, the first signal electrode 42 and the second signal electrode 44 are in the disconnected state, and the signal is blocked and cannot be transmitted to subsequent devices.

[0038] Reference Figure 5 When the switch is in the on state, there is an electric potential between the lower driving electrode 61 and the upper driving electrode 62. The piezoelectric ceramic 6 is deformed under the action of the electric potential, squeezing the silicon film at the upper end of the back cavity 7. The mercury droplet 5 moves to the bottom of the through groove 8. The mercury droplet 5 contacts the first signal electrode 42 and the second signal electrode 44. The first signal electrode 42 and the second signal electrode 44 are turned on, and the signal is transmitted to the subsequent device through the coplanar waveguide 4.

[0039] The above description is only a specific example of the present invention and does not constitute any limitation to the present invention. It is obvious that for professionals in this field, after understanding the content and principles of the present invention, they may make various modifications and changes in form and details without departing from the principles and structures of the present invention. However, these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A droplet radio frequency micro-electromechanical system switch based on piezoelectric ceramic film drive, comprising a lower substrate (1), an intermediate substrate (2) and an upper substrate (3), wherein the upper substrate (3) is provided with a first metal pad (9) and a second metal pad (10), and the lower substrate (1) is provided with a coplanar waveguide (4), wherein the coplanar waveguide (4) comprises a first ground electrode (41), a second ground electrode (43), a first signal electrode (42) and a second signal electrode (44), characterized in that: The upper and lower surfaces of the upper substrate (3) are respectively provided with a piezoelectric ceramic film (6) and a back cavity (7); The intermediate substrate (2) is provided with a through groove (8), the through groove (8) being located above the first signal electrode (42) and the second signal electrode (44), and partial areas of the first ground electrode (41) and the second ground electrode (43) are exposed in the through groove (8); The through groove (8) is aligned with the center of the back cavity (7) and is connected vertically, and contains a mercury droplet (5); The mercury droplet (5) located in the back cavity enters the through groove (8) in a small amount when the switch is closed, and enters the through groove (8) in a large amount when the switch is turned on, and contacts the first signal electrode (42) and the second signal electrode (44); The lower substrate (1), the middle substrate (2) and the upper substrate (3) are packaged as a whole.

2. The switch according to claim 1, characterized in that: A lower driving electrode (61) and an upper driving electrode (62) are deposited on the upper and lower surfaces of the piezoelectric ceramic film (6), respectively; the lower driving electrode (61) is connected to the first metal pad (9), and the upper driving electrode (62) is connected to the second metal pad (10).

3. The switch according to claim 1, characterized in that: The plane size of the intermediate substrate (2) is smaller than the plane size of the lower substrate (1), and is located in the middle of the lower substrate (1).

4. The switch according to claim 1, characterized in that: The plane size of the upper substrate (3) is the same as the plane size of the middle substrate (2), and during packaging, the upper substrate (3) and the middle substrate (2) are aligned on all sides.

5. The switch according to claim 1, characterized in that: The first signal electrode (42) and the second signal electrode (44) are located between the first ground electrode (41) and the second ground electrode (43), and are at the same distance from the two ground electrodes.

6. The switch according to claim 1, characterized in that: The lower substrate (1) is made of glass material; The intermediate substrate (2) is made of SU-8 photoresist material; The upper substrate (3) is made of single crystal silicon material.

7. The switch according to claim 2, characterized in that: The lower driving electrode (61) and the upper driving electrode (62) are made of alloy material; The first metal pad (9) and the second metal pad (10) are made of gold material.

Images