CN1295728C - Low valve valve DC-AC separable microelectronic mechanical switch and its producing method - Google Patents

Abstract

A low-threshold DC-AC separable microelectromechanical switch and a manufacturing method thereof are designed to realize a structure design of a low-threshold voltage DC-AC separable MEMS switch through the design of two driving electrodes. The manufacturing method is as follows: a. Chip: Clean the gallium arsenide substrate with concentrated HCL and ammonia water; b. Deposit and photolithographically coplanar waveguides and DC drive electrodes on the prepared substrate to generate the structure of the switch coplanar waveguide and DC drive electrodes; c. Growth dielectric protection layer: grow SiN insulating layer by PECVD process; d. Deposit and photolithography sacrificial layer: coat polyimide sacrificial layer on GaAs substrate and photolithography; e. Sputter upper plate on The Ti/Au/Ti bottom gold layer for electroplating is sputtered on the polyimide layer; f. photolithography and corrosion of the Ti/Au/Ti bottom gold layer to form corrosion holes; g. the Ti/Au/Ti bottom gold layer Layer gold plating; h. Release sacrificial layer: form a suspended movable membrane structure.

Description

Low-threshold DC-AC separable microelectromechanical switch and method of manufacturing the same

Technical field

The invention realizes the structural design of a MEMS switch with a low threshold voltage DC and AC separable through the design of two driving electrodes, and belongs to the technical field of micro-electromechanical systems (MEMS).

Background technique

MEMS switches have low insertion loss, high isolation, wide operating frequency band, easy integration with high-speed electronic devices and good linearity, and have been widely used in fields with strict weight and volume requirements such as radar and wireless communications. .

Compared with the series contact switch, the parallel capacitive membrane switch has the advantage of eliminating the contact loss and micro-connection force caused by the direct contact between the wires.

Traditional MEMS capacitive switches generally adopt a fixed-beam structure. MEMS switches with this structure have the following disadvantages: high threshold voltage. The threshold voltage of a MEMS capacitive switch with a normal size is about 20-50V, and DC and AC loaded on the same signal line.

Contents of Invention

Technical problem: The object of the present invention is to provide a low-threshold DC-AC separable MEMS switch with high reliability, high repeatability and low production cost and its manufacturing method.

Technical solution: The low-threshold DC/AC separable MEMS switch of the present invention is based on the substrate, a signal line of a coplanar waveguide is arranged in the middle of the substrate, and a coplanar waveguide is respectively arranged on both sides of the substrate The ground wire of the coplanar waveguide is provided with a DC drive electrode between the signal line of the coplanar waveguide and the ground wire of the coplanar waveguide, and an insulating layer is covered on the middle narrow band part of the DC drive electrode and the signal line of the coplanar waveguide. The upper part is provided with a movable membrane of the upper pole plate, and the two ends of the movable membrane of the upper pole plate are fixed on the ground of the coplanar waveguide, and there is a gap layer between the insulating layer and the movable membrane of the upper pole plate. A shallow groove can be arranged on the movable membrane of the upper pole plate as required.

The manufacturing method of the low-threshold DC/AC separable microelectromechanical switch of the present invention is realized based on the GaAs MMIC process, and its manufacturing method is:

a. Prepare the substrate: clean the gallium arsenide substrate with concentrated HCL and ammonia water, and observe whether the alignment mark of the stepper lithography machine on the returned throwing wafer is clear;

b. Deposit and lithographically coplanar waveguides and DC drive electrodes on the prepared substrate: on the gallium arsenide substrate, first sputter the AuGeNi/Au layer, then peel off the metal layer in the ultrasonic generator, and finally Coplanar waveguides that generate switches, and structures for DC-driven electrodes;

c. Growth dielectric protection layer: grow a SiN insulating layer by PECVD process on the signal line of the coplanar waveguide and the DC drive electrode, and perform photolithography;

d. Depositing and photoetching a sacrificial layer: coating a polyimide sacrificial layer on a GaAs substrate and photoetching, photoetching a polyimide sacrificial layer, only retaining the sacrificial layer under the movable film of the upper plate, and forming a dimple in the middle of the sacrificial layer;

e. Sputtering upper plate: sputtering Ti/Au/Ti base gold layer for electroplating on the polyimide layer;

f. Photoetching and corroding the Ti/Au/Ti bottom gold layer to form corrosion holes;

g. Electroplating gold on the Ti/Au/Ti bottom gold layer;

h. Release the sacrificial layer: first remove the remaining photoresist with acetone, then dissolve the polyimide sacrificial layer under the switch beam with a developer, and dehydrate with absolute ethanol. A suspended movable membrane structure is formed.

The criteria for distinguishing whether it is this structure are:

(a) The structure from top to bottom is the movable film of the upper plate; the gap layer; the insulating layer; the signal line of the coplanar waveguide, the ground line of the coplanar waveguide and the DC drive electrode; the substrate.

(b) Design two DC drive electrodes at both ends of the signal line of the fixed beam;

(c) A dimple can be designed on the movable membrane as required, so that the membrane can be in good contact with the insulating layer in the off state, and the stress of the membrane can be offset.

Satisfying the above structure is the structure we designed.

When the switch is turned on, the signal is directly output through the signal line, and when there is an external DC drive voltage, the switch beam is deflected under the action of electrostatic force. When the DC voltage increases to a certain value, the switch beam is in contact with the insulating layer and is in the off state. At this time, a large coupling capacitance is formed between the switch beam and the coplanar waveguide signal line, and the signal is coupled to the ground, and the switch is controlled by The "on" state changes to the "off" state.

Beneficial effect: compared with common membrane switch, the advantages of the present invention are:

1. The DC driving voltage of the switch can be loaded on the electrodes at both ends of the signal line, thereby reducing the threshold voltage;

2. DC and AC can be separated;

3. Improved the linearity of the switch;

4. This structure can be used in combination with flat membrane beams, folded beams and T-shaped beams;

5. No stickiness;

6. Dimples are used to deal with contact problems in the process;

7. Easy to manufacture single-pole multi-throw switches;

8. The manufacturing process is simple and compatible with GaAs MMIC process.

Based on the characteristics of the low-threshold DC-AC separable parallel membrane switch structure, the present invention solves the problem of high threshold voltage and DC-AC loading on the same signal line, and easily realizes high reliability and high repeatability of the device , low production cost, and well meet the basic requirements of microelectronic systems for devices. Therefore, the structure of the low-threshold DC-AC separable parallel membrane switch has good application value and broad market potential.

MEMS (micro-electro-mechanical systems) switches with low threshold voltage DC-AC separation have the following characteristics:

1. Low loss, high isolation, wide operating frequency band 2. Compatible with GaAs MMIC process and can also be integrated with high-speed electronic devices 3. Due to the design of two additional electrodes, it can reduce the switching threshold voltage and make the signal DC and AC are separated to improve the linearity of the switch. In addition, the manufacturing process of this low-threshold voltage MEMS switch is very simple. The invention solves many problems in the original realization of the MEMS switch structure in the aspects of material, process, reliability, repeatability and production cost.

Description of drawings

Figure 1 is a top view of a low-threshold DC-AC separation MEMS switch.

Figure 2 is a cross-sectional view of a low-threshold DC-AC separation MEMS switch.

Fig. 3 is a top view of a low-threshold DC-AC separation MEMS switch (with the upper film removed).

Figure 4 is a schematic diagram of the insertion loss and return loss of the switch.

Figure 5 is a schematic diagram of the isolation and return loss of the switch.

Fig. 6 is a cross-sectional view of a dimpled membrane switch.

Figure 7 is a top view of a dimpled membrane switch.

Specific implementation plan

The low-threshold DC-AC separable MEMS switch of the present invention uses a substrate 7 as a base, a coplanar waveguide signal line 4 is provided in the middle of the substrate 7, and a coplanar waveguide is respectively provided on both sides of the substrate 7 The ground wire 6 of the coplanar waveguide is provided with a DC drive electrode 5 between the signal line 4 of the coplanar waveguide and the ground wire 6 of the coplanar waveguide, and the upper part of the middle narrowband part of the DC drive electrode 5 and the signal line 4 of the coplanar waveguide is covered with insulation Layer 3, upper plate movable film 1 is arranged on the upper part of the insulating layer 3, and the two ends of the upper plate movable film 1 are fixed on the ground wire 6 of the coplanar waveguide, and the insulating layer 3 and the upper plate movable film 1 is interstitial layer 2. A shallow groove 8 may be provided on the movable membrane 1 of the upper plate.

The specific process steps and parameters of the low-threshold DC-AC separable MEMS switch based on the GaAS process are as follows:

1. Prepare the substrate: Since the substrate of the micromechanical switch is a gallium arsenide throwback wafer, it must be cleaned with concentrated HCL and ammonia water. At the same time, pay attention to observing the alignment mark of the stepper lithography machine on the throwback wafer Is it clear.

2. Deposition and photolithography of coplanar waveguides and DC drive electrodes: on the gallium arsenide substrate, first sputter the 800/300/2200A AuGeNi/Au layer, then peel off the metal layer in the ultrasonic generator, and finally A switched coplanar waveguide, and DC drive electrode (5) structure is generated. The size of the coplanar waveguide is 84-140-84um, the length of the uneven area is 340um, and the size of the coplanar waveguide in the uneven area is 300-140-300um.

3. Growth dielectric protection layer: On the signal line of the coplanar waveguide and the DC drive electrode, a 1000A SiN insulating layer is grown by PECVD process on the fixed beam, and photolithography is performed. The width of the insulating layer is 120um.

4. Depositing and photoetching a sacrificial layer: Coating a polyimide sacrificial layer on a GaAs substrate and performing photolithography. The thickness of the polyimide sacrificial layer determines the switch plate gap, which is selected as 2um. This can change the thickness of the sacrificial layer by adjusting the speed of the spinner and the concentration of the polyimide solution. Photoetching the polyimide sacrificial layer, leaving only the sacrificial layer under the switch beam, and forming a dimple in the middle of the beam to form a good contact in the off state.

5. Sputtering upper plate: sputtering bottom gold Ti/Au/Ti=500/1500/300A for electroplating on the polyimide layer

6. Photoetching and etching the Ti/Au/Ti bottom gold layer to form corrosion holes with a size of 8×8um,

7. Gold electroplating: electroplate gold on the Ti/Au/Ti bottom gold layer in 55 cyano solution, the thickness of the electroplated gold layer is 1.4um, the beam length L is 380um, and the beam width is 60um.

8. Release the sacrificial layer: first remove the residual photoresist with acetone, then dissolve the polyimide sacrificial layer under the switch beam with a developer, and dehydrate with absolute ethanol. A suspended switch beam structure is formed.

In addition, some problems need to be paid attention to in the whole technical solution, including: the design of the driving electrode and the size of the coplanar waveguide, which is very important for the realization of the overall device structure, the size of the threshold voltage, and the nonlinear characteristics. ; The selection of the sacrificial layer, which determines the roughness of the released surface and the off-state capacitance value, is related to the isolation of the switch; a shallow concave can be designed on the upper plate film to make the upper plate dimpled to offset The residual stress of the membrane makes the membrane in good contact with the lower plate in the off state and improves the isolation; the upper plate membrane can use a flat membrane, or a folded beam or a T-beam to further reduce the threshold voltage of the switch.

Throughout the process of realizing the low-threshold DC-AC separable MEMS switch, there is no special material or complicated special process, and it is completely compatible with the GaAs MMIC process. Therefore, the application of the low-threshold DC-AC separable MEMS switch structure of the present invention can reduce the threshold voltage of the switch, realize DC-AC separation, and improve the characteristics of the switch.

Claims (3)

1, the DC-AC separable microelectronic mechanical switch of a kind of low threshold value, it is characterized in that this microelectronic mechanical switch is substrate with substrate (7), be provided with the holding wire (4) of a co-planar waveguide in the centre of substrate (7), be respectively equipped with the ground wire (6) of a co-planar waveguide on the both sides of substrate (7), between the ground wire (6) of the holding wire (4) of co-planar waveguide and co-planar waveguide, be provided with DC driven electrode (5), covering insulating barrier (3) on the middle arrowband part of the holding wire (4) of DC driven electrode (5) and co-planar waveguide, be provided with the movable film of top crown (1) on the top of insulating barrier (3), the two ends of the movable film of top crown (1) are fixed on the ground wire (6) of co-planar waveguide, are clearance layer (2) between insulating barrier (3) and the movable film of top crown (1).

2, the DC-AC separable microelectronic mechanical switch of low threshold value according to claim 1 is characterized in that being provided with a shallow grooves (8) on the movable film of top crown (1).

3, the manufacture method of the DC-AC separable microelectronic mechanical switch of a kind of low threshold value as claimed in claim 1 is characterized in that the realization of this microelectronic mechanical switch based on GaAs technology, and its manufacture method is:

A, preparation substrate: clean gallium arsenide substrate (7) with dense HCL and ammoniacal liquor, observe back the alignment mark of throwing the stepping mask aligner on the sheet whether clear;

B, go up deposit and photoetching co-planar waveguide and DC driven electrode (5): on gallium arsenide substrate (7) at the substrate of preparing (7), the sputter AuGeNi/Au of elder generation layer, in ultrasonic generator, peel off this metal level then, generate the structure of the co-planar waveguide and the DC driven electrode (5) of switch at last;

E, somatomedin protective layer: holding wire (4) and DC driven electrode (5) at co-planar waveguide are gone up the insulating barrier with pecvd process growth SiN, and photoetching;

D, deposit and photoetching sacrifice layer: go up coating polyimide sacrifice layer and photoetching at GaAs substrate (7), the photoetching polyimide sacrificial layer only keeps the sacrifice layer under the movable film of top crown (1), and forms a scrobicula in the middle of sacrifice layer;

E, sputter top crown: the Ti/Au/Ti bottom layer that sputter is used to electroplate on polyimide layer;

F, photoetching are also corroded the Ti/Au/Ti bottom layer, form etch pit;

G, at Ti/Au/Ti bottom layer electrogilding;

H, releasing sacrificial layer: remove residual photoresist with acetone earlier, use the polyimide sacrificial layer under the developing solution dissolution switch beam then, and, form movable film (1) structure that suspends with the absolute ethyl alcohol dehydration.

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