CN109979768B

CN109979768B - RF MEMS switch based on ultra-smooth structure

Info

Publication number: CN109979768B
Application number: CN201910234436.XA
Authority: CN
Inventors: 杨德智; 张清卿
Original assignee: Beijing Tsitec Co ltd
Current assignee: Shenzhen Qingli Technology Co ltd
Priority date: 2019-03-26
Filing date: 2019-03-26
Publication date: 2020-11-17
Anticipated expiration: 2039-03-26
Also published as: CN109979768A

Abstract

The invention provides an RF MEMS switch and a realization method thereof. The RF MEMS switch comprises a substrate, a fixed part, a movable part and a driving part, wherein the fixed part, the movable part and the driving part are horizontally arranged on the substrate, the movable part comprises a self-supporting part and a slidable part, the self-supporting part is composed of self-recoverable graphite islands, and the driving part can drive the slidable part to move on the self-supporting part in the horizontal direction, so that contact electrodes matched with the fixed part and the movable part are used for realizing the switch. The present invention has a longer life span and more stable device performance because the slidable portion is always supported by the self-supporting portion and uses van der waals force as a restoring force, thus avoiding deformation from gravity and mechanical fatigue.

Description

RF MEMS switch based on ultra-smooth structure

Technical Field

The invention belongs to the technical field of radio frequency micro-electro-mechanical system switches (RF MEMS Switch), and particularly relates to an RF MEMS Switch based on a super-smooth structure and an implementation method thereof.

Background

With the development of radar and wireless communication technologies, small-sized, low-power consumption, high-performance, and multifunctional radio frequency devices are becoming the development trend in the radio field, radio frequency devices are developing towards miniaturization and integration, and MEMS switches are coming, and RF MEMS switches have gradually replaced the conventional GaAs FET switches and become the development direction of radio frequency switches (RF switches). Compared with the traditional switch, the RF MEMS switch has the advantages of lower insertion loss, higher isolation, better linearity, lower power consumption, smaller volume and the like, can be easily integrated with an IC circuit, and has wide application prospect.

At present, the existing RF MEMS switches mainly include an electrostatic driving mechanism, a thermal driving mechanism, an electromagnetic driving mechanism, a piezoelectric driving mechanism, and the like in terms of driving modes; the device structure has two main flow modes, namely a cantilever beam mode and a bridge mode. The existing RF MEMS switches have common defects in their structure, no matter which kind of drive is used: one is that the movable parts of the existing devices are all suspended, and are easily deformed under the influence of gravity under the condition of long-term use; secondly, the restoring force of the existing device is elastically restored by depending on the mechanical strength of the MEMS device (by using the principle similar to a spring), and the existing device is easy to generate fatigue and further generate deformation under the condition of long-term use.

Prior art cantilever and bridge RF MEMS switches are shown in fig. 1(a), 1(b), 1(c), 2(a), 2(b), 2(c), respectively. The suspended cantilever beam and the bridge are dragged by gravity in the two states of opening and closing to finally cause deformation; meanwhile, the cantilever beam and the bridge are deformed after fatigue is generated by means of self mechanical recovery, and the deformation changes the distance between the movable part and the fixed part, so that the design response speed, the loss, the Q value and the like are influenced, and finally, the performance of the RF MEMS switch is reduced and even loses efficacy.

The art has provided solutions to this problem, such as increasing the dimensions of the cantilever beam and the bridge, which results in devices with increased mechanical strength to resist deformation; or the distance between the movable part and the fixed part of the switching device is enlarged to reserve a deformation margin, but the performance of the device is sacrificed in the case of doing so, the former prevents further miniaturization of the device and the latter reduces the response speed of the device.

Disclosure of Invention

The invention provides an RF MEMS switch structure with a brand-new structure, which utilizes a structure ultra-sliding technology to arrange two electrodes of a switch in a movable part and a fixed part respectively, wherein the movable part and the fixed part are arranged horizontally, the movable part is self-supported in the vertical direction, gravity deformation is avoided, the movable part realizes self-recovery by utilizing Van der Waals force between graphite crystal sheet layered structures, and the fatigue condition does not exist.

The movable part in the structure is composed of self-recoverable graphite islands, and the self-recoverable graphite islands comprise a slidable part and a self-supporting part, wherein the slidable part and the self-supporting part have almost zero friction and zero loss, so that the mechanical loss of the device is nearly zero and the device is hardly abraded.

Specifically, the RF MEMS switch structure provided by the invention is as follows:

an RF MEMS switch structure comprises a substrate, a fixed part, a movable part and a driving part, wherein the fixed part, the movable part and the driving part are horizontally arranged on the substrate, the movable part comprises a self-supporting part and a slidable part, the self-supporting part is composed of self-recoverable graphite islands, the driving part can drive the slidable part to move on the self-supporting part in the horizontal direction, and a contact electrode matched between the fixed part and the movable part is used for realizing switching.

Preferably, the fixing portion includes a fixing portion contact electrode.

Preferably, the movable part comprises a metal cover located over the slidable part.

Preferably, a movable portion contact electrode is formed over the metal cover.

Preferably, the driving part includes a driving electrode.

Preferably, the driven electrode is formed over the metal cover.

Preferably, an insulating layer is formed between the driven electrode and the movable portion contact electrode.

Preferably, an insulating layer is formed between the metal cover and the driven electrode or the movable portion contact electrode.

Preferably, the driving manner of the driving electrode to drive the driven electrode is selected from electrostatic driving, thermal driving, electromagnetic driving or piezoelectric driving.

Preferably, the self-recoverable graphite islands are formed using the following process:

1. the sample was selected as a ZYB grade HOPG and a new surface was mechanically peeled off in an ultra clean room.

2. And (3) on the newly stripped surface, a layer of glue of an LOR model is paved by using a glue evening machine, then a ZEP model glue is paved, and then the ZEP glue above the designed graphite island layout is exposed.

3. And washing the LOR glue above the graphite island layout by using acetone.

4. And etching the sample in an etching environment with oxygen ions to remove residual glue above the graphite island.

5. And evaporating a layer of metal titanium or metal chromium above the graphite island for a connecting layer, and then evaporating a layer of metal Au on the connecting layer.

6. The LOR gel was washed off in the areas outside the graphite islands at this time using lift-off technology.

7. And (3) placing the sample in an etching environment with oxygen ions, and etching to obtain the self-recoverable graphite island.

Through the technical scheme, the RF MEMS switch provided by the invention has the following advantages:

(1) the structure of horizontal contact is adopted, so that the deformation caused by gravity can be completely avoided;

(2) the van der waals force between graphite layers is used as restoring force, so that the deformation of a movable part caused by mechanical fatigue is completely avoided;

(3) by utilizing the structure ultra-smooth technology, almost no friction loss and almost no abrasion are generated, so that the formed RF MEMS switch has longer service life and more stable device performance.

Drawings

FIGS. 1(a), 1(b), and 1 (c): cross-sectional views of prior art cantilever beam RF MEMS switch structures; FIG. 1(a) is an ON state, and FIG. 1(b) is an OFF state; FIG. 1(c) shows the switch in a sagging state after fatigue deformation;

fig. 2(a), 2(b), 2 (c): cross-sectional views of prior art bridge RF MEMS switch structures; FIG. 2(a) is an ON state, and FIG. 2(b) is an OFF state; FIG. 2(c) shows the switch in a sagging state after fatigue deformation;

fig. 3(a), 3 (b): the cross section of the RF MEMS switch structure in the embodiment 1 of the application; FIG. 3(a) is a schematic diagram of an ON state, and FIG. 3(b) is a schematic diagram of an OFF state;

FIG. 4: a schematic diagram of a manufacturing process of the self-recoverable graphite island;

fig. 5(a), 5 (b): the self-recoverable schematic diagram of the self-recoverable graphite island, fig. 5(a) is a schematic diagram of the probe driving the graphite island to slide along the super-slip shear plane, and fig. 5(b) is a schematic diagram of the self-recoverable graphite island after the probe is removed.

Reference numerals: 100 is a base, 200 is a contact metal, 300 is an upper and a lower electrode, 400 is a signal transmission line, 500 is a thermal resistor, 1 is a substrate, 2 is a self-supporting portion, 3 is a slidable portion, 4 is a metal cover, 5 is a first insulating layer, 6 is a driven electrode, 7 is a second insulating layer, 8 is a movable portion contact electrode, 9 is a fixed portion contact electrode, and 10 is a driving electrode. 101 is a graphite substrate, 501 is a probe.

Detailed Description

Embodiment 1 of the present invention will be further described with reference to the accompanying drawings:

referring to fig. 3(a), 3(b), the present invention provides an RF MEMS switch including a substrate 1, a fixed portion, a movable portion and a driving portion horizontally arranged on the substrate 1; wherein the fixed portion comprises a fixed portion contact electrode 9; wherein the driving portion comprises a driving electrode 10; wherein the movable part comprises a self-supporting part 2 and a slidable part 3, which are composed of self-recoverable graphite islands; a metal cover 4 is formed on the slidable portion 3, and the metal cover 4 is an optional structure and may be omitted; a driven electrode 6 and a movable portion contact electrode 8 are formed on the metal cover 4; a second insulating layer 7 is formed between the driven electrode 6 and the movable-portion contact electrode 8, and the driven electrode 6 is located above the movable-portion contact electrode 8 in this embodiment 1, and the positions of these two layers can be exchanged in practice; a first insulating layer 5 is formed between the metal cover 4 and the driven electrode 6 or the movable portion contact 8. Wherein the preferred size of the ultra-smooth structure is 3um-30 um. Further preferably, the diameter or side length thereof is 10um to 30 um.

The working principle of the device is as follows:

by applying a signal to the driving electrode 10 located above the substrate 1, the driven electrode 6 can be driven to move in the horizontal direction, and the driven electrode 6 thereby drives the slidable portion 3 and the movable portion contact electrode 8 to move in the horizontal direction, so that the movable portion contact electrode 8 and the fixed portion contact electrode 9 are in contact (i.e., the switch is in an off state). When the supply of the electric signal to the driving electrode 10 is stopped, the driven electrode 6 is no longer driven, the slidable portion 3 generates a return movement on the self-supporting portion 2 to return to the original state, and the slidable portion 3 thereby drives the movable portion contact electrode 8 to be separated from the fixed portion contact electrode 9 (i.e., the switch is in the on state).

The driving method that can be adopted by the present invention is various, and although the method shown in example 1 adopts the electrostatic driving method, it is possible to adopt thermal driving, magnetoelectric driving, and piezoelectric driving. For example, the magnetoelectric drive can be easily realized by changing the drive electrode in embodiment 1 into the drive magnetic pole and the driven electrode into the driven magnetic pole.

The self-recoverable graphite island comprises a slidable part 3 and a self-supporting part 2 which are made of the same material and are made of graphite. For example, one of the forming processes can be seen in fig. 4, which includes the following specific steps:

2. And (3) paving a layer of glue with LOR model of 200-300 nm on the newly stripped surface by using a glue homogenizing machine, and then paving a layer of glue with ZEP model of 400-500 nm.

3. Exposing the ZEP glue above the designed graphite island layout, and washing the LOR glue above the graphite island layout with acetone.

4. And (3) placing the sample in an etching environment with oxygen ions for 3-10 seconds (etching by oxygen plasma), and removing residual glue above the graphite island.

5. And evaporating a layer of metal titanium or metal chromium with the thickness of 25-50 nm above the graphite island for a connecting layer, and then evaporating a layer of metal Au with the height of 100-200 nm on the basis.

6. Removing the stripping photoresist, the electron beam photoresist and the metal in the area except the graphite island by using a lift-off process to form a patterned metal cover layer;

7. and finally, placing the sample in an etching environment with oxygen ions (reactive ion etching), and obtaining the self-recoverable graphite islands with different heights according to different etching time, wherein the maximum self-recoverable graphite island edge obtained by etching by the method is as long as 30um, and the maximum self-recoverable graphite island height can be 5 um.

A partial enlarged schematic view of the self-recoverable graphite island formed by the above process is shown in fig. 5. in fig. 5, it can be seen that sliding occurs between the slidable and self-supporting sections if a force in the horizontal direction is applied between the slidable and self-supporting sections, since the two planes in which relative movement occurs are graphite layers, which causes the above-described sliding between the different graphite sheets. The self-recovery occurs when the horizontal force disappears, because the van der waals force between the graphite layers exceeds the frictional resistance between the graphite layers, and the sliding graphite sheet is pulled back by the van der waals force. The graphite sheet can have a high response speed because the movement direction of the graphite sheet when retracting is opposite to the direction of the graphite sheet when sliding out, and the speed is extremely high.

The RF MEMS switch provided by the invention provides a brand new framework, a horizontal contact structure is adopted, and the slidable part is always supported by the self-supporting part, so that the deformation caused by gravity can be completely avoided; the invention also utilizes Van der Waals force between graphite layers as restoring force, thus completely avoiding the deformation of the movable part caused by mechanical fatigue; the sliding between the slidable part and the self-supporting part is the sliding between the graphite layers, and almost no friction loss and almost no abrasion exist, so that the RF MEMS switch provided by the invention has longer service life and more stable device performance. Meanwhile, the Van der Waals force response time is extremely short, so that the response speed of the device can be greatly improved, and the method is particularly suitable for application scenes with higher frequency.

The above description is only a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above embodiment, but equivalent modifications or changes made by those skilled in the art according to the present disclosure should be included in the scope of the present invention as set forth in the appended claims.

Claims

1. An RF MEMS switch structure characterized by: the movable part comprises a self-supporting part and a slidable part, wherein the self-supporting part is composed of self-recoverable graphite islands, the slidable part can be driven by the driving part to move on the self-supporting part in the horizontal direction, and therefore contact electrodes used between the fixed part and the movable part in a matched mode realize switching.

2. The RF MEMS switch structure of claim 1, wherein: the fixing portion includes a fixing portion contact electrode.

3. The RF MEMS switch structure of claim 1, wherein: the movable portion includes a metal cover over the slidable portion.

4. The RF MEMS switch structure of claim 3, wherein: a movable portion contact electrode is formed over the metal cap.

5. The RF MEMS switch structure of claim 1, wherein: the driving portion includes a driving electrode.

6. The RF MEMS switch structure of claim 4, wherein: a driven electrode is formed over the metal cap.

7. The RF MEMS switch structure of claim 6, wherein: an insulating layer is formed between the driven electrode and the movable portion contact electrode.

8. The RF MEMS switch structure of claim 6, wherein: an insulating layer is formed between the metal cover and the driven electrode or the movable portion contact electrode.

9. The RF MEMS switch structure of claim 6, wherein: the driving part comprises a driving electrode, and the driving electrode drives the driven electrode in a driving mode selected from electrostatic driving, thermal driving, electromagnetic driving or piezoelectric driving.

10. A process for forming self-recoverable graphite islands for RF MEMS switch structures according to any of claims 1 to 9, comprising the steps of:

(1) mechanically stripping the ZYB grade HOPG to a new surface in an ultra clean room;

(2) spreading a layer of LOR type glue on the newly stripped surface by using a glue spreader, then spreading a ZEP type glue, and then removing the ZEP glue above the designed graphite island layout in an exposure mode;

(3) washing the LOR glue above the graphite island layout by using acetone;

(4) etching in an etching environment with oxygen ions to remove residual glue above the graphite island;

(5) evaporating a layer of metal titanium or metal chromium above the graphite island, and then evaporating a layer of metal Au on the basis;

(6) washing off LOR glue in the area except the graphite island by using lift-off technology;

(7) and etching in an etching environment with oxygen ions to obtain the self-recoverable graphite island.