# US 2013/0157005 A1 · Method for Wafer-Level Surface Micromachining to Reduce Stiction

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- Number: US 2013/0157005 A1
- Document ID: US20130157005A1
- Status: Published application
- Kind: A1
- Application number: 13/331,582
- Filed: 2011-12-20
- Published: 2013-06-20
- Earliest claimed: 2011-12-20
- Assignees: Analog Devices, Inc.
- Inventors: Fang Liu; Kuang Yang
- Web page: https://patentgrep.com/patent/US20130157005A1

## CPC

- B81B 3/001: {Structures having a reduced contact area, e.g. with bumps or with a textured surface}
- B81B 3/0005: {Anti-stiction coatings}
- B81B 3/0018: {Structures acting upon the moving or flexible element for transforming energy into mechanical movement or vice versa, i.e. actuators, sensors, generators}
- B81C 2201/112: Depositing an anti-stiction or passivation coating, e.g. on the elastic or moving parts
- Y10T 428/24355: Continuous and nonuniform or irregular surface on layer or component [e.g., roofing, etc.]
- Y10T 428/24521: with component conforming to contour of nonplanar surface
- B81B: MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES (piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/00, H10N35/00)
- B81C: PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS (making microcapsules or microballoons B01J13/02; processes or apparatus specially adapted for the manufacture or treatment of piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/01)
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

An array of microbumps with a layer or coating of non-superhydrophobic material yields a superhydrophobic surface, and may also have a contact angle hysteresis of 15 degrees or less. A surface with such an array may therefore be rendered superhydrophobic even though the surface structure and materials are not, by themselves, superhydrophobic.

## Claims

### Claim 1

A micromachined device having a superhydrophobic surface, the superhydrophobic surface including a surface treatment of a non-superhydrophobic material, the micromachined device comprising:
a substrate having a first surface;
a movable mass having an opposing surface, the opposing surface separated from the first surface by a gap;
at least one of the first surface and the opposing surface having an array of bumps extending into the gap, the array comprising:
a plurality of bumps having a pitch of between 0.5 microns and 30 microns, and each bump having a height of at least 0.2 microns and width of at least 0.5 microns, and
a layer of non-superhydrophobic material covering the array.

### Claim 2 (depends on 1)

The micromachined device of claim 1, wherein each bump has a height of not more than 8 microns, and a width of not more than 20 microns.

### Claim 3 (depends on 2)

The micromachined device of claim 2, wherein in the array comprises bumps of uniform dimensions.

### Claim 4 (depends on 2)

The micromachined device of claim 2, wherein in the array comprises bumps of non-uniform dimensions.

### Claim 5 (depends on 1)

The micromachined device of claim 1, wherein the spacing of the bumps is uniform.

### Claim 6 (depends on 1)

The micromachined device of claim 1, wherein the spacing of the bumps is non-uniform.

### Claim 7 (depends on 1)

The micromachined device of claim 1, wherein each of the first surface and the opposing surface include a superhydrophobic array.

### Claim 8 (depends on 1)

The micromachined device of claim 1, wherein the non-superhydrophobic material comprises fluorine.

### Claim 9 (depends on 1)

The micromachined device of claim 1, wherein the non-superhydrophobic material comprises chlorine.

### Claim 10 (depends on 1)

The micromachined device of claim 1, wherein the non-superhydrophobic material comprises methane.

### Claim 11 (depends on 1)

The micromachined device of claim 1, wherein the non-superhydrophobic material comprises a one of a perflourodecyltrichlorosilane coating or a phenyl-based coating.

### Claim 12 (depends on 1)

The micromachined device of claim 1, at least a portion of the covered array is superhydrophobic.

### Claim 13

A method of forming a superhydrophobic surface, the method comprising:
providing a surface;
providing an array of microbumps on the surface, wherein the array by itself is not superhydrophobic, and wherein the array comprises:
a plurality of microbumps having a pitch of between 0.5 microns and 30 microns, and each bump having a height of at least 0.2 microns and width of at least 0.5 microns, and
coating the array of microbumps with a non-superhydrophobic material,
wherein the coating renders the array is superhydrophobic.

### Claim 14 (depends on 13)

The method of claim 13, wherein coating the array of microbumps with a non-superhydrophobic material comprises coating the array of microbumps with a material selected from the group of fluorine, chlorine, methane, a phenyl-based material, and a perflourodecyltrichlorosilane material.

### Claim 15

A method of fabricating a micromachined device having a superhydrophobic surface, the method comprising:
providing a substrate having a first surface;
adding a sacrificial layer on the first surface, the sacrificial layer having an exposed surface;
etching an array of cavities into the exposed surface of the sacrificial layer;
depositing a low surface-free-energy layer to the array of cavities, the low surface-free-energy material lining but not filling the cavities in the array of cavities such that the cavities are lined cavities;
depositing a mass layer on the low surface-free-energy layer, such that the sacrificial layer and the low surface-free-energy layer are sandwiched between the substrate and an opposing surface of the mass layer, the mass layer occupying the plurality of lined cavities and forming a plurality of bumps; and
removing the sacrificial layer;
wherein the bumps protrude from the opposing surface of the mass layer in the direction of the substrate, and wherein the array has a contact angle of at least 140 degrees and a contact angle hysteresis of less than 15 degrees.

### Claim 16 (depends on 15)

The method of fabricating a micromachined device having a superhydrophobic surface of claim 15, wherein depositing a low surface-free-energy layer to the sacrificial layer comprises depositing a material selected from the group of fluorine, chlorine, methane, a phenyl-based material, and a perflourodecyltrichlorosilane material.

### Claim 17

A method of fabricating a micromachined device having a superhydrophobic surface, the method comprising:
providing a substrate having a first surface;
providing an array of bumps on the first surface;
adding a low surface-free-energy layer to the array, such that the low surface-free-energy layer coats the bumps but does not fill the space between the bumps;
adding a sacrificial layer on the low surface-free-energy layer, the sacrificial layer having an exposed surface;
depositing a mass layer on the exposed surface of the sacrificial layer such that the sacrificial layer is sandwiched between the substrate and an opposing surface of the mass layer; and
removing the sacrificial layer, thereby exposing the coated array,
wherein the bumps of the array protrude from the substrate in the direction of the opposing surface of the mass layer, and wherein the array has a contact angle of at least 140 degrees and a contact angle hysteresis of less than 15 degrees.

### Claim 18 (depends on 17)

The method of fabricating a micromachined device having a superhydrophobic surface of claim 17, wherein the array of bumps comprises a plurality of bumps having a pitch of between 0.5 microns and 30 microns, and each bump having a height of at least 0.2 microns and width of at least 0.5 microns.

### Claim 19 (depends on 17)

The method of fabricating a micromachined device having a superhydrophobic surface of claim 17, wherein adding a low surface-free-energy layer to the array comprises adding a material selected from the group of fluorine, chlorine, methane, a phenyl-based material, and a perflourodecyltrichlorosilane material.

### Claim 20 (depends on 17)

The method of fabricating a micromachined device having a superhydrophobic surface of claim 17, the method further comprising, before depositing a mass layer on the exposed surface of the sacrificial layer:
etching an array of cavities into the exposed surface of the sacrificial layer;
depositing a second layer of low surface-free-energy material to the array of cavities, the low surface-free-energy material lining but not filling the cavities in the array of cavities such that the cavities are lined cavities,
wherein depositing the mass sandwiches the sacrificial layer and the second low surface-free-energy layer between the substrate and an opposing surface of the mass layer, the mass layer occupying the plurality of lined cavities and forming a plurality of bumps, and wherein removing the sacrificial layer exposes an array of bumps coated with the second low surface-free-energy material.