Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1996-11-12
2001-03-20
Robinson, Ellis (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S069000, C428S413000, C428S414000, C428S416000, C428S418000, C053S079000
Reexamination Certificate
active
06203869
ABSTRACT:
BACKGROUND
The present invention relates generally to getters for removing hydrogen from sealed microelectronic packages, and the like, and more particularly, to a composite film hydrogen getter for removing hydrogen from sealed microelectronic packages backfilled with an inert gas, and to a metal foil or thin metal film hydrogen getter that catalyzes the reaction of hydrogen with backfilled air or oxygen.
The deleterious effects of hydrogen on the performance of various types of electronic devices, such as gallium arsenide (GaAs) and related compound semiconductor devices, is well known. Hydrogen is capable of entering the crystal structure of these materials and wherein band-gap trap states are formed that limit the carrier lifetime of the devices. Thus, compound semiconductor devices suffer degraded electrical performance when operated at normal operating temperatures in an atmosphere that includes hydrogen. Therefore, reliable operation of such devices requires the removal or exclusion of hydrogen from the surrounding atmosphere. In addition, ferroelectric materials such as strontium bismuth tantalate or strontium bismuth tantalate niobate, for example, are sensitive to and degrade in the presence of small amounts of hydrogen.
Strontium bismuth tantalate (SBT), bismuth strontium tantalate niobate (SBTN), lead zirconate titanate (PZT) and many high temperature superconductors containing bismuth are all sensitive to small amounts of hydrogen at elevated temperatures. Ferroelectric memory devices containing these materials have failed at temperatures of 125° C. with less than 100 PPM hydrogen. The same parts are stable for extended periods at 125° C. when exposed to air (0.5 PPM hydrogen). For military and for an increasing segment of the commercial market survivability at 125° C. is mandatory.
The accumulation of hydrogen gas is particularly problematic in hermetically-sealed device packages. While hermetically-sealed packaging offers its contents protection against oxygen, water vapor, and other harmful contaminants present in the atmosphere, it also serves to retain and accumulate internally generated contaminants. Hydrogen outgasses from such devices and is accumulated within the hermetic packaging and invades semiconductor lattices of the device. Once in place, the hydrogen acts as a dopant that alters the response characteristics of the device in erratic ways. Hydrogen concentrations of 0.1% by volume (1000 PPM) dramatically alter the response characteristics of semiconductor devices, and hydrogen concentrations on the order of 0.5% by volume (5000 PPM) have been observed in hermetic packages after extended periods.
The present invention was developed specifically as a hydrogen gettering material for sealed microelectronic packages containing ferroelectric memory devices containing SBT and SBTN. While many vacuum gettering materials are commercially available and were evaluated for use, none were found to getter hydrogen sufficiently to protect the ferroelectric material. Conventional gettering materials do not work with sealed microelectronic packages primarily because they do not specifically getter hydrogen, but also getter other gases as well.
U.S. patent application Ser. No. 08/629,286, filed Apr. 8, 1996, entitled “Thin Film-Coated Foil Getters for Hydrogen in Electronic Device Packages” assigned to the assignee of the present invention provides for the use of a palladium (Pd) coated gettering metal, such as zirconium (Zr), titanium (Ti) for example, as a hydrogen getter. The gettering material disclosed in this patent application relies on the specificity of the clad (coated) material to diffuse hydrogen while not diffusing nitrogen or other elements, which permits the gettering metal to getter only hydrogen. These coated gettering metals were placed in sealed microelectronic packages backfilled with nitrogen and were tested, but they did not work sufficiently well to remove all the hydrogen from the sealed package in the presence of the nitrogen. Consequently, the electronic circuit in the microelectronic package degraded over time.
Powdered palladium oxide (PdO) has been used as a hydrogen getter material in dewars, for example. The difficulty with powdered palladium oxide gettering material is that the powder is loose in the package (i.e., not attached to the package). One embodiment of the present invention solves this problem. Another embodiment of the present invention capitalizes on the ability of certain metals to catalyze the reaction of hydrogen and oxygen to form water. Specifically this invention provides a palladium film in an oxygen containing package to getter the hydrogen by producing water.
Accordingly, it is an objective of the present invention to provide for a composite film hydrogen getter for removing hydrogen from sealed microelectronic packages backfilled with an inert gas. It is another objective of the present invention to provide for a metal foil or thin metal film hydrogen getter that catalyzes the reaction of hydrogen with backfilled air or oxygen.
SUMMARY OF THE INVENTION
To meet the above and other objectives, the present invention provides for a thin film hydrogen getter comprising a reactive composite film made of a hydrogen reactive material, such as palladium oxide powder, for example, that is deposited or otherwise disposed in an inert material or matrix, such as an epoxy resin, for example. The composite thin film hydrogen getter thus formed may be cut into or fabricated as small pieces that may be placed in a sealed microelectronic package or other sealed container, that houses an integrated circuit, and that may optionally be backfilled with an inert gas such as nitrogen. The hydrogen reactive material, or active ingredient, reacts with hydrogen within the sealed package, which typically outgasses from the package. The getter keeps hydrogen in the sealed package from reacting with the hydrogen sensitive materials in the integrated circuit, even in the absence of oxygen.
The present thin film getter thus provides a means for removing hydrogen from a sealed container, and specifically one that has been backfilled with an inert gas, and has been shown to work well with nitrogen. While powdered palladium oxide has been used to getter hydrogen in dewars, the present invention uses palladium oxide in a form that is suitable for use in sealed microelectronic packages and other sealed containers.
Other embodiments of the present invention capitalize on the ability of certain metals to catalyze the reaction of hydrogen and oxygen to form water. Specifically this embodiment of the present invention provides a palladium film in an oxygen containing package to getter the hydrogen by producing water. Palladium and other metals catalyze to decompose diatomic hydrogen producing reactive monatomic hydrogen. The reactive hydrogen reacts quickly with oxygen to produce water.
Thus, the present invention provides for a gettering system for use in sealed microelectronic packages containing hydrogen sensitive materials such as SBTN, and the like. Use of the present invention allows active ferroelectric materials and integrated circuits to survive under sealed packaging conditions. The scope and utility of the present invention thus enhances commercially manufactured semiconductor and ferroelectric devices.
The present invention also provides for methods for fabricating a sealed package containing the hydrogen getter. An enclosure is provided and a microelectronic device is disposed in the enclosure with the getter. The getter may comprise several different embodiments. The first embodiment comprises a layer of inert material and a hydrogen reactive material that is imbedded in or attached thereto. A second embodiment provides for hydrogen reactive material that is secured to a portion of the adhesive used to attach the microelectronic device to the enclosure, for example. A third embodiment attaches a metal foil to the enclosure using the same adhesive used to attach the microelectronic device to the enclosure. A fourth embodiment provides for t
Dougherty Thomas K.
Dyer Venita L.
Ramer O. Glenn
Alkov Leonard A.
Figueroa John J.
Lenzen, Jr. Glenn H.
Raufer Colin M.
Robinson Ellis
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