Michael Deeds

Nano-to-millimeter scale integrated systems

Over the last several years various industries have been developing nano, micro, and millimeter scale technologies, which have resulted in components ranging from quantum transistors, to widely commercialized integrated circuits, to microelectromechanical sensors. A common emphasis of these fabrication industries has been on the integration of different functions in miniaturized systems; however, the technology currently used to realize these systems is monolithic. A unique class of hybrid technology systems is Integrated nano to millimeter (In2m) systems. An In2m system typically has components spanning multiple sizes, diverse technology domains, and mixtures of electrical, mechanical, thermal, chemical, fluidic, and biological functions.

Reliability assessment of delamination in chip-to-chip bonded MEMS packaging

The bond layer is often the weakest link in the reliability of chip packages in the integrated circuit (IC) industry. Micro-electrical-mechanical systems (MEMS) packages are no exception to this trend. This paper presents a nondestructive methodology for determining delamination in chip-to-chip bonded MEMS. Experimental methods are used to determine the adhesive layer strength in samples subjected to environmental testing, and the reliability of the bonding layer is investigated. A simulation is performed using inputs from scanning acoustic microscopy, and simulation model results are correlated with the experimental die shear measurements to establish the validity of the nondestructive methodology for determining adhesive layer strength.

Delamination study of chip-to-chip bonding for a LIGA-based safety and arming system

The development of a miniature underwater weapon safety and arming system requires reliable chip-to-chip bonding of die that contain microelectromechanical actuators and sensors fabricated using a LIGA MEMS fabrication process. Chip-to- chip bonding is associated for several different bond materials (indium solder, thermoplastic paste, thermoplastic film and epoxy film), and bonding configurations (with an alloy 42 spacer, silicon to ceramic, and silicon to silicon). Metrology using acoustic micro imaging has been developed to determine the fraction of delamination of samples.

MOEMS chip-level optical fiber interconnect

A package design, fabrication process, and assembly process to hermetically seal the microstructure area of a microoptoelectromechanical system (MOEMS) at the chip level is presented and evaluated. The packaged chip is fabricated using the Bosch deep reactive ion etching (DRIE) process on silicon on insulator (SOI) substrates. The packaging structures are formed during the batch fabrication of the MOEMS device. A hermetic seal is formed via an indium solder ring around the perimeter of the MOEMS chip that span channels etched in the silicon for optical fibers. The seal is made between the device chip, metallized optical fibers, and a cap chip with a fluxless soldering process. The integrity of the package is evaluated through die shear, fiber pull, and highly accelerated life testing (HALT).

Mechanical Response of Silicon MEMS Diaphragms to Applied Pressure

The response of silicon-based MEMS diaphragms to applied pressure was studied to determine their ability to effectively measure the extent of blast overpressure. Different pressures (0-100 psi) were applied to silicon diaphragms of different diameters (1200, 1500, and 2200 μm) to study their mechanical response under both static and dynamic conditions using experimental and finite element analysis. A laser triangulation sensor was used to determine the diaphragm displacement as a function of blast pressure. High speed camera images were obtained to understand the response of the diaphragm at an applied blast pressure. Results show consistent behavior for deflections (10, 14, and 26 μm, respectively, at 40 psi) under dynamic conditions. Finite element analysis indicates that the dynamic deflection is larger than the corresponding static deflection for the same applied pressures. Burst strengths were not consistent, although the diaphragms fractured at their circumferential edges and showed a small degree of plastic deformation. It also appears that the diaphragm manifests a hemispherical as well as a conical deflection depending on applied blast pressures.

Packaging of a MEMS based safety and arming device

Packaging of MEMS devices introduces new challenges to the package architecture. MEMS systems introduce new interfaces, processes, and materials foreign to the IC packaging industry. To build reliable MEMS systems, failure modes must be activated and understood. In addition, the metrology techniques must be developed to interrogate critical aspects of the package. The system presented in this paper is a MEMS based safety and arming device (S&A) for underwater weapons. Critical components, packaged in various hermetic and non-hermetic configurations, are cycled through a series of metrologies and environmental conditioning.

Thermal Analysis of MEMS Actuator Performance

A MEMS based device consisting of microactuators was modeled using finite element analysis. The temperature profile of the complete package was obtained and compared to experimental measurements. Good agreement was found between the modeling and measurements. Parametric studies of potential design parameters of the chip package to decrease the power requirements to the actuators have been studied. Increasing the gap between the handle layer and the device layer of the SOI (silicon on insulator) chip from 2 to 3 microns resulted in a reduction of 10% (0.2 Watts) per beam of the actuator. A glass top chip proved to be better at reducing the power requirements for the actuators when compared to a silicon top chip. Modeling shows that relief cuts in the substrate had a larger effect on the power reduction compared to those on the top chip since the heat conduction path to the substrate is a lower resistance path. The power reduction was as high as 50% (1.1 Watts) per beam of the actuator, when the relief cut in the substrate was 50 microns.Copyright

Test and evaluation of chip-to-chip attachment of MEMS devices

In the IC industry, the bond layer serves as the foundation and often the weak link in the reliability of chip packages. MEMS packages are likely to have a greater number of bond layers with more stringent requirements. The additional bond layers arise from multiple interfaces inside the package. The bond layers in MEMS devices often must maintain precise component or chip alignment. In addition, the bond layers may have to withstand loading from both the macroenvironment and loading within the package. This paper presents the bond requirements for a MEMS based Safety and Arming (S&A) device. The S&A system requires precise alignment between a micromachined silicon chip, a patterned Alumina ceramic chip, and a deflection delimiter. Several candidate designs were subjected to a series of environmental tests including thermal cycling, accelerated stress tests, mechanical shock, and combinations of the above conditions. A Scanning Acoustic Microscope (SAM) is utilized to measure initial delamination and to identify incremental damage due to environmental exposure. The tests are ultimately used to rank the suitability of the bond layer material for chip-to-chip attachment with large coefficient of expansion differences. Tested bond materials include epoxy, thermoplastic, and solder.

Fluxless optical fiber attachment for hermetic MOEMS applications

Fluxless soldering is desirable for the hermetic packaging of micro-optoelectromechanical (MOEMS) systems, especially those used in harsh environments, or those that require very long shelf-life. An example of such a microsystem is a safe & arm (S&A) MEMS device that requires reliable operation over 20 to 30 years. For this application, degradation and out-gassing of the organic materials, such as those contained in fluxes and epoxies could result in the contamination and stiction of the moving microparts. In this paper we present simulation and experimental results of using a diode laser to attach and seal fiber optic feed-throughs to a kovar carrier package. In order to obtain reliable fluxless solder joints, certain environmental conditions namely, an inert and/or reducing gas environment needs to be present during the process. In addition, the solder and substrate surfaces must be sufficiently free of oxides and organic contaminants. Acceptable process parameters such as the laser power density, spot size, and duration, package geometry have been determined both experimentally and through simulation. It has been established that oxygen levels less than 0.04% (400 ppm) obtained inside a glove-box obtained using inert gas (100% N2 or 95%N2, 5% H2) is necessary to achieve adequate joints