Brian H. Stark

A passive wireless integrated humidity sensor

This paper presents a single-chip integrated humidity sensor (IHS) capable of wireless operation through inductive coupling with a remote transmitter. The 1.5/spl times/0.5/spl times/8mm/sup 3/ sensor chip consists of a planar electroplated copper coil (20 /spl mu/m thick, 30 /spl mu/m pitch, and 23 turns) and a silicon substrate separated by a 4100-5600 /spl Aring/ polyimide film. The resonant frequency of the IHS changes with humidity and the measured sensitivity ranges from 4-16 kHz/%RH. Measurements show a hysteresis of 4.5%RH over a range of 30-70%RH for a 5600 /spl Aring/-thick polyimide film IHS.

A low-temperature thin-film electroplated metal vacuum package

This paper presents a packaging technology that employs an electroplated nickel film to vacuum seal a MEMS structure at the wafer level. The package is fabricated in a low-temperature (<250/spl deg/C) 3-mask process by electroplating a 40-/spl mu/m-thick nickel film over an 8-/spl mu/m sacrificial photoresist that is removed prior to package sealing. A large fluidic access port enables an 800/spl times/800 /spl mu/m package to be released in less than three hours. MEMS device release is performed after the formation of the first level package. The maximum fabrication temperature of 250/spl deg/C represents the lowest temperature ever reported for thin film packages (previous low /spl sim/400/spl deg/C). Implementation of electrical feedthroughs in this process requires no planarization. Several mechanisms, based upon localized melting and Pb/Sn solder bumping, for sealing low fluidic resistance feedthroughs have been investigated. This package has been fabricated with an integrated Pirani gauge to further characterize the different sealing technologies. These gauges have been used to establish the hermeticity of the different sealing technologies and have measured a sealing pressure of /spl sim/1.5 torr. Short-term (/spl sim/several weeks) reliability data is also presented.

A micromachined Pirani gauge with dual heat sinks

This paper reports a micromachined Pirani gauge with dual heat sinks that can be integrated with microelectromechanical systems (MEMS) devices inside a vacuum package to monitor long-term pressure changes and stability inside the package. The Pirani gauge utilizes small gaps (<1 /spl mu/m) between its heater and two thermal heat sinks to obtain large dynamic range (20 mtorr to 2 torr) and high sensitivity (3.5/spl times/10/sup 5/ (K/W)/torr). The gauge is 2/spl times/2 mm/sup 2/ in size, is fabricated using the dissolved wafer process (DWP) on a glass substrate, and utilizes dielectric bridges for signal routing. Measurements show the low end of the dynamic range can be extended by reducing the gap distance between the heater and thermal sinks, which matches well with analytical modeling. This gauge shows an uncertainty of 50 /spl mu/torr and a detectable leak rate of 3.1/spl times/10/sup -16/ cm/sup 3//s, assuming a common micropackage volume of 1.6/spl times/10/sup -5/ cm/sup 3/, which represents at least four orders of magnitude improvement over traditional leak testing.

A doubly anchored surface micromachined Pirani gauge for vacuum package characterization

This paper presents a surface micromachined Pirani gauge for measuring vacuum pressure inside sealed micro cavities. This thin gap (800nm) SiO/sub 2//Si/sub 3/N/sub 4//SiO/sub 2/ gauge can measure absolute pressure from atmospheric to less than 1mTorr without sophisticated interface electronics by using a reliable software calibration technique. This allows the sensor to be integrated with common vacuum packaging technologies to measure leak rates as low as 10/sup -17/cm/sup 3//s. This represents a 5 order of magnitude improvement over traditional helium leak testing with a substantially reduced cost.

An Ultra-Thin Hermetic Package Utilizing Electroplated Gold

This paper reports development and characterization of a novel technology for ultra-thin hermetic biocompatible packages at the wafer level and presents data demonstrating the hermeticity of the package. This technology utilizes a 3-micron thick film of gold that is electroplated over a 2-micron thick polyimide layer to completely enclose a section of an implantable system, which may contain integrated electronics. This package was implemented on an implantable probe substrate to demonstrate a future application of the technology, with a yield of 88%. This technology was further characterized through the development of an integrated saline sensor, which predicted a MTTF of 160 years when soaking in Phosphate Buffered Saline.

A passive humidity monitoring system for in-situ remote wireless testing of micropackages

This paper reports a small passive wireless humidity monitoring system (HMS) for continuous monitoring of humidity changes inside miniature hermetic packages, presents its application in determining hermeticity of an implantable biomedical package, and presents long-term performance results obtained from packages implanted in guinea pigs. This 7/spl times/1.2/spl times/1.5 mm/sup 3/ system consists of a high-sensitivity capacitive humidity sensor that forms an LC tank circuit together with a hybrid coil wound around a ferrite substrate. The resonant frequency of the circuit changes when the humidity sensor capacitance changes in response to changes in humidity. The HMS can resolve humidity changes of /spl plusmn/2.5%RH over a 2 cm range. The resolution is sufficient enough to monitor internal package humidity for either in in-vitro or in-vivo testing.

The fabrication of all-diamond packaging panels with built-in interconnects for wireless integrated microsystems

To explore polycrystalline diamond (poly-C) as a packaging material for wireless integrated microsystems (WIMS), a new fabrication technology has been developed to fabricate thick WIMS packaging panels with built-in interconnects. An ultrafast poly-C growth technique, used in this study, involves electrophoresis seeding and filling of dry-etched Si channels by undoped poly-C followed by removal of Si. A second layer of highly B-doped poly-C, which acts as a built-in interconnect, is deposited on the backside of undoped poly-C layer. The lowest resistivity values demonstrated on control samples are in the range from 0.003 to 0.31 /spl Omega/-cm. The results show that, by increasing the poly-C growth areas through the use of 2-/spl mu/m-wide Si channels, the poly-C growth time can be reduced by a factor in the range from 2.75 to 10.5 depending upon the aspect ratio of Si channels. The poly-C packaging technology, which is expected to provide new structures/concepts in MEMS/WIMS packaging, is being reported for the first time.

An integrated process for post-packaging release and vacuum sealing of electroplated nickel packages

This paper presents a packaging technology that employs a thick nickel film to vacuum seal a MEMS structure at the wafer level. The package is fabricated in a 3-mask process by electroplating a 40-micron thick nickel film over an 8-micron sacrificial photoresist that is removed prior to package sealing. The large fluidic access port enables an 800/spl times/800 /spl mu/m package to be released in less than three hours. Implementation of electrical feedthroughs in this process requires no planarization. Device release is performed after the formation of the first level package. Several mechanisms, based upon localized melting and Pb/Sn solder bumping, for sealing low fluidic resistance feedthroughs have been investigated. This package has been fabricated with an integrated Pirani gauge to further characterize the different sealing technologies. These gauges have been used to establish the hermeticity of the different sealing technologies and have measured a sealing pressure of /spl sim/1.5Torr.

A Wafer-Level Vacuum Packaging Technology Utilizing Electroplated Nickel

In recent years, there has been an increasing demand for low temperature (<400°C) packaging technologies that can vacuum seal MEMS devices at the wafer level with a minimal amount of wasted die area. Several emerging classes of devices require wafer-level vacuum packaging. There has been growing development of micro-resonators for RF communications systems [1]. The devices require the high Q-factor performance generated by vacuum sealing in order to function as highly selective filters and oscillators. There has also been considerable development in the field of resonant gyroscopes [2], which also require a low pressure ambient for optimal performance. The rapid development of MEMS devices requiring low cost vacuum packaging has outpaced the development of suitable sealing technologies.Copyright

A mold and transfer technique for lead-free fluxless soldering and application to MEMS packaging

This paper demonstrates a technique to premold and transfer lead-free solder balls for microelectrocmechanical systems (MEMS)/electronics packaging applications. A reusable bulk micromachined silicon wafer is used to mold a solder paste and remove excess flux prior to transfer to a host wafer that may contain released MEMS. This technique has been used to fabricate low temperature thin film MEMS vacuum packages. Long term (>5 months) reliability of these packages at room temperature and pressure is demonstrated through integrated Pirani gauges. These packages have survived over 600 hours in an autoclave (130degC, 85% RH, 2 atm) and more than 1300 temperature cycles (55degC to 125degC)