MEMS wafer level package

• US 6,452,238 B1
• Filed: 09/27/2000
• Issued: 09/17/2002
• Est. Priority Date: 10/04/1999
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Orcutt, John W., Dewa, Andrew Steven, Lin, Tsen-Hwang
• Primary Examiner(s): Meier, Stephen D.
• Application Number:
  US09/671,487
• Time in Patent Office: 720 Days
• Field of Search: 257/415, 257/414, 257/532
• US Class Current: 257/415
• CPC Class Codes: B81B 7/007 Interconnections between the MEMS and external electrical signals
• CPC Class Codes: G01P 1/023 for acceleration measuring devices
• CPC Class Codes: H01L 2224/05599 Material
• CPC Class Codes: H01L 2224/45015 being circular
• CPC Class Codes: H01L 2224/45099 Material
• CPC Class Codes: H01L 2224/48247 connecting the wire to a bond pad of the item
• CPC Class Codes: H01L 2224/48465 the other connecting portion not on the bonding area being a wedge bond, i.e. ball-to-wedge, regular stitch
• CPC Class Codes: H01L 2224/85399 Material
• CPC Class Codes: H01L 23/10 characterised by the material or arrangement of seals between parts, e.g. between cap and base of the container or between leads and walls of the container
• CPC Class Codes: H01L 24/48 of an individual wire connector
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/00014 the subject-matter covered by the group, the symbol of which is combined with the symbol of this group, being disclosed without further technical details
• CPC Class Codes: H01L 2924/01046 Palladium [Pd]
• CPC Class Codes: H01L 2924/01078 Platinum [Pt]
• CPC Class Codes: H01L 2924/01079 Gold [Au]
• CPC Class Codes: H01L 2924/10253 Silicon [Si]
• CPC Class Codes: H01L 2924/14 Integrated circuits
• CPC Class Codes: H01L 2924/181 Encapsulation
• CPC Class Codes: H01L 2924/207 Diameter ranges
• CPC Class Codes: H01L 2924/30107 Inductance

Abstract

An improved wafer level encapsulated micro-electromechanical device fabricated on a semiconductor wafer and a method of manufacture using state-of-the-art wafer fabrication and packaging technology. The device is contained within a hermetic cavity produced by bonding a silicon wafer with active circuits to an etched silicon wafer having cavities which surround each device, and bonding the two wafer by either thin film glass seal or by solder seal. The etched wafer and thin film sealing allow conductors to be kept to a minimum length and matched for improved electrical control of the circuit. Further, the device has capability for a ground ring in the solder sealed device. The devices may be packaged in plastic packages with wire bond technology or may be solder connected to an area array solder connected package.

Claims

1. A micro-electromechanical wafer level encapsulated device, comprising:

a plurality of devices fabricated on a semiconductor substrate wafer,

a cap wafer fabricated from a silicon wafer, and an array of cavities of predetermined height etched in a pattern corresponding to the active devices on said substrate wafer, and a thin film of glass covering the unetched area,

a hermetic seal produced by bonding the cap wafer to the semiconductor wafer using said thin film glass as a bonding agent such that each of said discrete devices is sealed in a cavity of predetermined dimensions,

at least one conductor formed on the surface of the substrate wafer which provides electrical coupling to each device fabricated on the substrate wafer, and

an array of holes fabricated in the cap wafer which provides access to each of said conductors from outside the cavity.

2. A micro-electromechanical device as in claim 1 wherein the device comprises an RF switch.

3. A micro-electromechanical device as in claim 1 wherein said conductors have equal length and resistivity.

4. A micro-electromechanical device as in claim 1 wherein said glass is in the range of 0.5 to 5.0 microns in thickness.

5. A micro-mechanical device as in claim 1 wherein walls of said cavity comprise silicon in the range of 0.05 to 0.2 mm thickness.

7. A micro-electromechanical wafer level encapsulated device, as in claim 1 wherein said device comprises multiple chips.

6. A RF switch micro-electromechanical wafer level encapsulated device, comprising:

a plurality of devices fabricated on a semiconductor substrate wafer,

a cap wafer fabricated from a silicon wafer having an array of cavities of predetermined height etched in a pattern corresponding to each of the active devices on said substrate wafer, the walls of said cavities being in the range of 0.05 to 0.2 mm in thickness, and a thin film of glass in the range of 0.5 to 5.0 microns thickness covering the unetched area,

a hermetic seal produced by bonding the cap wafer to the semiconductor wafer using said thin film glass as a bonding agent such that each discrete device is sealed in a cavity of predetermined dimensions,

one or more conductors of equal length and resistivity formed on the surface of the substrate wafer which provides electrical coupling to each device fabricated on the substrate wafer,

an array of holes fabricated in the cap wafer which provides access to each of said conductors from outside the cavity.

8. A plastic encapsulated micro-electromechanical device comprising;

a semiconductor device encapsulated within a cavity in a silicon cap, wherein said cap is bonded to the device substrate by a thin film of glass,

one or more conductors on the device substrate electrically coupled to the device and extending outside the encapsulated cavity, and each of which is accessible by a hole in the cap,

wire bonds connections between each of said conductors and a lead frame,

and said devices are encapsulated in a plastic molding compound.

9. A micro-electromechanical wafer level encapsulated device, comprising:

a plurality of devices fabricated on a semiconductor substrate wafer,

a cap wafer fabricated from a silicon wafer, having an array of cavities of predetermined height etched in a pattern corresponding to the active devices on said substrate wafer, and a film of solder adhered to a layer of solder compatible metal covering the unetched area,

at least one conductor formed on the surface of the substrate wafer which provides electrical coupling to each device fabricated on the substrate wafer, said conductors further covered by a dielectric film, and a solder compatible metal layer,

a hermetic seal produced by bonding the cap wafer to the semiconductor wafer using said solder as a bonding agent such that the device is sealed in a cavity of predetermined dimensions, and

an array of holes fabricated in the cap wafer which provides access to each of said conductors from outside the cavity.

10. A micro-electromechanical device as in claim 9 having a solder ball attached to each conductor through said holes in the cap.

11. A micro-electromechanical device as in claim 9 having an electrical ground ring surrounding each discrete device produced by metal layers on the cap.