Multilayer thin film hydrogen getter

Abstract

A thin film hydrogen getter is provided for protecting GaAs circuitry sealed in an hermetic package. The thin film getter which comprises a multilayer metal film which is deposited by vacuum evaporation techniques onto a surface of the packaging. The multilayer film comprises (1) a titanium film and (2) palladium film which is deposited onto the titanium film. Both the titanium and the palladium are deposited during the same coating process run, thereby preventing the titanium from being oxidized. The palladium continues to prevent the titanium from being oxidized once the getter is exposed to the atmosphere. However, hydrogen is easily able to diffuse through the palladium into the titanium where it is chemically bound up, since palladium is highly permeable to hydrogen. If EMI shielding is desired, a conductive metal, such as aluminum or copper, can first be formed between the packaging and the titanium layer.

Description

[0001] The present application is related to application Serial No. ______, filed on ______ and entitled "Dielectric Interconnect Frame Incorporating EMI Shield and Hydrogen Absorber for Tile T / R Modules" [PD-00W125]. That application is directed to dielectric interconnect frames, used in GaAs hermetically-sealed packaging.[0002] The present invention relates to packaging of gallium arsenide (GaAs) integrated circuits, and, more particularly, to a hydrogen getter for chemically binding up hydrogen evolved from packaging materials.[0003] Gallium Arsenide (GaAs) integrated circuits which are hermetically packaged will suffer from reduced performance and reliability if the hydrogen that is evolved from the packaging materials is allowed to diffuse into the GaAs devices. Hydrogen concentrations as low as 500 ppm have been demonstrated to decrease the mean time to failure. A prior art solution to this problem of hydrogen poisoning is to insert a material into the package which chemically...

AI Technical Summary

Benefits of technology

[0009] The thin film getter of the present invention comprises a multilayer metal film which is vacuum-deposited. The multilayer film comprises (1) a titanium film and (2) palladium film which is deposited onto the titanium film. Both the titanium and the palladium are deposited during the same coating process (vacuum deposition) run, thereby preventing the titanium from being oxidized. The palladium continues to prevent the titanium from being oxidized once the getter is exposed to the atmosphere. However, hydrogen is easily able to diffuse through the palladium into the titanium where it is chemically bound up, since palladium is highly permeable to hydrogen. The present inventors have demonstrated high hydrogen absorption rates and hydrogen capacities for thin film getters deposited onto plastic test parts.

[0011] There appears to be no other hydrogen getter which is produced entirely by vacuum deposition techniques and has the unique multilayer structure consisting of a 40 to 80 microinch layer of titanium followed by an 8 microinch thick protective layer of palladium. The palladium film, which prevents oxidation of the titanium while at the same time allowing hydrogen to easily pass through, is considered to be one of the most important novel features of the present invention.

[0014] The palladium continues to prevent the titanium from being oxidized once the getter is exposed to the atmosphere, while the metal film below, e.g., aluminum or copper, provides an excellent high electrical conductance metal for ground shield. The getter acts to absorb hydrogen, as described above. In addition to the advantages described above for the getter, the ground / EMI shield can be used to enhance circuit performance.

Problems solved by technology

Gallium Arsenide (GaAs) integrated circuits which are hermetically packaged will suffer from reduced performance and reliability if the hydrogen that is evolved from the packaging materials is allowed to diffuse into the GaAs devices.

There are several disadvantages to this getter: (1) in order to provide enough hydrogen absorption capacity in a package, a significant volume of silicone getter must be used; (2) Residual Gas Analysis (RGA), used to determine internal contaminants within a hermetic package, can return false results related to moisture content when the silicone product is used; (3) silicone oil migration within the package has been observed, which makes re-work of the assembly impossible, due to the inability to re-solder joints wetted with the silicone oil; (4) there is added cost and complexity associated with having to bond the silicone getter sheet to some available surface; and (5) the silicone getter must first be vacuum baked at 150.degree. C. for greater than 16 hours before it can be inserted into the package.

This adds to the manufacturing time and cost.

These getters did not provide good reliable gettering capability, most likely due to the oxide layer present on the titanium foil.

A titanium foil would also have the added cost of welding to the package lid.

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