Electronic devices such as integrated circuits are often packaged in hermetically sealed enclosures. These enclosures protect the device from contaninants, particles, and water vapor that would otherwise enter the package and mechanically damage or electrically disrupt the device. The hermetic packages, however, do not perfectly seal out these elements over the life of the device. Additionally, some water vapor and debris is present in the enclosure cavity when the enclosure is sealed, or evolved by the packaging materials as the materials cure.
Getters, compounds that capture contaminants, moisture vapor, and particles, are included inside the device enclosures to trap these species and preclude degradation of device performance, thereby increasing the operational lifetime of the device. Various getter compounds are available depending on the environment to which the getter will be subjected.
Existing getter compounds are unsatisfactory for use with many modem micromechanical devices. Micromechanical devices are small structures typically fabricated on a semiconductor wafer using techniques such as optical lithography, doping, metal sputtering, oxide deposition, and plasma etching which have been developed for the fabrication of integrated circuits. Typical micromechanical devices include accelerometers, pressure sensors, micro-motors, and microrirrors.
Because of their small size, often less than 100 microns, micromechanical devices are very susceptible to damage from debris inside the micromechanical device package. For example, debris can easily obstruct the motion of, or electrically short-circuit, micromirror elements which are often no larger than 17 microns.
Many micromechanical devices include moving components that place unique demands on surface lubrication and passivation systems. For example, the deflectable element of a micromirror device rotates about a torsion beam hinge axis and is stopped by contact with a landing zone or spring structure. The contact point experiences metal-to-metal contact and some scrubbing action. This metal-to-metal contact can create sticking and friction (stiction) between the moving components. Stiction is caused by the capillary action of water vapor present on the surface, van der Waals attraction, and intermetallic bonding of the metals. Stiction becomes worse as the contacting surfaces wear against each other since the contact area is increased.
Passivation coatings on micromirror devices reduce stiction and wear between the contacting surfaces. One passivation material that is especially useful for micromirror devices is perfluorodecanoic acid (PFDA). PFDA, as taught by U.S. Pat. No. 5,331,454, issued Jul. 19, 1994 and entitled Low Voltage Reset for DMD, provides an oriented monolayer on the surfaces of the DMD. The oriented monolayer provides a chemically inert surface that reduces the stiction between adjacent metal parts.
Unfortunately, the PFDA forms a relatively weak bond between with the aluminum surfaces on which it is deposited. Because of the weak bond between the PFDA and the aluminum surfaces of the micromirror device, the scrubbing action between contacting parts wears the oriented monolayer and exposes the underlying aluminum. Without replenishment, exposed aluminum regions grow and eventually create unacceptably large stiction forces--ruining the device.
As taught in U.S. Pat. No. 5,939,785 entitled Micromechanical Device Including Time-Release Passivant, and U.S. patent application Ser. No. 60/105,269, entitled Getter for Enhanced Micromechanical Device Performance, a getter compound is included in the sealed enclosure containing the device. A getter compound is chosen that reversibly combines with the lubricant, generally a perfluoroalkanoic acid such as perfluorodecanoic acid (PFDA). Thus, the getter acts as a reservoir to source and store PFDA while maintaining a PFDA vapor within the package. The PFDA vapor condenses onto exposed surfaces of the device to maintain the monolayer.
PFDA is presently placed in the device package by a remote vapor deposition process described in U.S. patent application Ser. No. 60/102,438, entitled Surface Treatment Material Deposition and Recapture. As described therein, the lubricant is evaporated into a carrier gas and transported by the carrier gas to a heated deposition chamber. Once in the deposition chamber, the lubricant condenses out of the carrier gas forming a monolayer on the devices in the deposition chamber. The carrier gas also forms a monolayer on the surfaces of any ductwork and the deposition chamber itself.
While an improvement over prior systems, the vapor deposition and recapture process can be wasteful of the lubricant and require extensive periodic maintenance. For example, if the ductwork and deposition chamber are not kept sufficiently warm, large quantities of the lubricant will condense out of the carrier gas, clogging the deposition system and requiring the system to be disassembled and cleaned. What is needed is an improved method of delivering lubricant to the micromechanical device package that is not wasteful of the lubricant and does not require complex delivery mechanisms.