Vacuum encapsulation for surface acoustic wave (SAW) devices

Claim 2

A vacuum encapsulated surface acoustic wave (SAW) structure, comprising: a SAW device including a substrate of desired material having a major surface on which electro-acoustic transducers and associated electrical conductors are disposed along an acoustic wave propagation path on said substrate, said transducers and propagation path defining an active signal region on said major surface, said electrical conductors providing electrical connections for external signals presented to and received from the active signal region; and a cover, formed of material having substantially the same thermal characteristics and the same crystallographic orientation as the material comprising said substrate, said cover being bonded through a vacuum tight seal to said major surface of said substrate to enclose said active signal region in a vacuum environment.

Claim 3

The structure of claim 1, wherein said cover is orientated on said major surface such that the crystallographic axes of said cover material is in alignment with that of said substrate material.

Claim 4

The structure of claim 2, wherein said cover is formed of the same material as that comprising said substrate.

Claim 5

The structure of claim 1, wherein said cover is bonded to said major surface with a vacuum tight glass seal.

Claim 6

The structure of claim 4, wherein said vacuum tight glass seal is a glass frit seal.

Claim 7

A vacuum encapsulated surface acoustic wave (SAW) structure comprising: a SAW device including a substrate of desired material having a major surface on which electro-acoustic transducers and associated electrical conductors are disposed along an acoustic wave propagation path on said substrate, said transducers and propagation path defining the surface area of an active signal region on said major surface, said electrical conductors providing electrical connections for external signals presented to and received from the active signal region; and a cover, including a spacer assembly portion and a cap assembly portion each formed of material having substantially the same thermal characteristics and crystallographic orientation as the material comprising said substrate material, said spacer portion having a central aperture extending between an upper surface and a bottom surface thereof, said aperture having a minimum cross section area equal to the surface area of said active signal region, said spacer portion being positioned on said major surface to enclose said active signal region within said central aperture, and being bonded along its bottom surface to said major surface with a vacuum tight glass seal, said cap portion being bonded in position to said upper surface of said spacer with a vacuum tight metal seal to enclose said active signal region in a vacuum environment within said central aperture.

Claim 8

A vacuum encapsulated surface acoustic wave (SAW) structure comprising: a SAW device including a substrate of desired material having a major surface on which electro-acoustic transducers and associated electrical conductors are disposed along an acoustic wave propagation path on said substrate, said transducers and propagation path defining the surface area of an active signal region on said major surface, said electrical conductors providing electrical connections for external signals presented to and received from the active signal region; and a cover, including a spacer assembly portion and a cap assembly portion each formed of material having substantially the same thermal characteristics and crystallographic orientation as the material comprising said substrate material, said spacer portion having a central aperture extending between an upper surface and a bottom surface thereof, said aperture having a minimum cross section area equal to the surface area of said active signal region, said spacer portion being positioned on said major surface to enclose said active signal region within said central aperture, and being bonded along its bottom surface to said major surface with a vacuum tight glass seal, said cap portion being bonded in position to said upper surface of said spacer with a vacuum tight metal seal to enclose said active signal region in a vacuum environment within said central aperture.

Claim 9

The structure of claim 6, wherein said spacer and said cap portions are further positioned to provide orientation of the material crystallographic axes of each with that of said substrate material.

Claim 10

The structure of claim 7, wherein said spacer and said cap assembly portions are formed of the same material as that comprising said substrate.

Claim 11

The structure of claim 6, wherein said transducers and said associated electrical conductors comprise metallized aluminum deposited on said major surface, wherein said electrical conductors are deposited at a greater coating thickness than said transducers along the portion of the conductors extending through said glass seal.

Claim 12

In the vacuum encapsulation of a surface acoustic wave (SAW) device having a substrate of desired material, the method of minimizing strain produced in the substrate material by thermal expansion and contraction of a vacuum encapsulating structure, comprising the steps of: forming the vacuum encapsulating structure from material having substantially the same thermal characteristics and substantially the same crystallographic orientation as that of the substrate material; positioning the encapsulating structure on the substrate to provide alignment of the crystallographic axes of each; and bonding the encapsulating structure to the substrate in a vacuum environment.

Claim 13

In the vacuum encapsulation of a surface acoustic wave (SAW) device having a substrate of desired material, the method of minimizing strain produced in the substrate material by thermal expansion and contraction of a vacuum encapsulating structure, comprising the steps of: forming the vacuum encapsulating structure from material having substantially the same thermal characteristics and substantially the same crystallographic orientation as that of the substrate material; positioning the encapsulating structure on the substrate to provide alignment of the crystallographic axes of each; and bonding the encapsulating structure to the substrate in a vacuum environment.

Claim 14

The method of claim 10, wherein the vacuum encapsulating structure is formed from material identical to that of the substrate material.

Claim 17

The method of claim 12, wherein the spacer and cap portions of the cover assembly are fabricated from the same material as that comprising the substrate.

Claim 18

The method of claim 12, wherein the step of bonding is provided by forming the glass seal using a glass frit.

Claim 19

The method of claim 12, further comprising between the steps of bonding and sealing, the step of: baking the SAW device with the bonded spacer, and the cap portion at an accelerated temperature in a vacuum environment to eliminate out-gassing from each.

Claim 20

The method of claim 15, further comprising between the steps of bonding and baking, the step of: cleaning the SAW device with the bonded spacer in an ultra-violet ozone cleaning tank to remove organic impurities.

Claim 21

The method of claim 12, further comprising prior to the step of forming, the step of: depositing the electrical conductors on the major surface such that the coating thickness of the conductors along that portion which passes through the glass seal is at a greater value than that of the transducers.