Ian R. Harvey

Micro-structure mechanical failure characterization using rotating Couette flow in a small gap

A new method for testing the failure rates of micro-mechanical structures is presented. The technique uses Couette flow in a narrow-gap channel to induce different forces and loading on an array of structures. The Couette flow is induced by a rotating disc, which allows multiple devices to be tested at different designed stress levels depending on rotation speed and radial position. As an example, SU-8 micro-structures are used to present a general testing procedure that can be applied to other components. The forces acting on the micro-structures are due to fluid shear stress, centrifugal forces from rotation and form drag, all of which are characterized as they vary with radial position for one rotation rate. One series of tests with a single circumferential row of identical micro-structures is performed to determine the relative importance of these forces on revolutions to failure and failure rate of the structures in the row. Two additional series of tests are conducted to determine the effects of also adding unsteady loading from wakes to the structures. This unsteady loading from wakes is induced by time-varying velocity and pressure variations, which are imposed when additional rows of micro-structures are placed at smaller radial positions compared to the row being tested. Weibull failure rate approaches are used to provide information on failure rate as dependent upon cumulative revolutions. As such, the testing approach is useful for failure characterization of thin-film adhesion, self assembled nano-layers and micro-mechanical structures.

Out-of-Plane MEMS Actuation Using a Scanning Electron Microscope

In the world of micro-electromechanical systems (MEMS) R&D efforts are expended creating new means of actuation, usually trading either force or displacement. In our scheme we pump charge into an electrically isolated conductive system with a Scanning Electron Microscope (SEM) to achieve a net force away from the substrate. Though we observe a highly dynamic response, we have approximated the force of the system with a quasi-static mechanical force sensor. The study of this actuation has focused on a spiral spring fabricated in Sandia Ultra-planar Multi-level MEMS Technology (SUMMiT-V™). Experiments show the effect of SEM beam conditions on this device, most notably finding the operation to begin at 5 keV accelerating voltage, where our Monte Carlo simulation predicts the beam will begin penetrating the 0.3 μm thick polySi. The out-of-plane motion has been measured as high as 220 μm which is approximately 2/3 of the diameter of the 2D spiral. A linear elastic model of the force sensor shows that in mechanical equilibrium the deflection is associated with an equivalent uniform pressure up to 90 Pa.Copyright

Biomimetic accommodating lens with implementation in MEMS

We describe an accommodating lens patterned after the crystalline lens of the eye. Our biomimetic MEMS design calls to mind the zonules of zinn which pull radially to stretch the crystalline lens of the eye to modify the optical path. We present initial characterization of the prototype macro-scale device constructed through traditional machining techniques and using a PDMS polymer lens. Testing of the macro-scale lens indicated a 22% change in focal length through the range of radial stretching, with degradation of the spherical lens shape but no hysteresis after low-cycle testing. We also demonstrate a MEMS implementation of the lens actuator constructed using the Sandia SUMMiT-V ™ surface micromachining process. The optical path of this system is approximately 300 microns in diameter, providing a platform to potential applications improving mobile camera optics and medical imaging.

Miniaturized camera system using advanced packaging techniques

Recent years have shown the tremendous need for visual recording in consumer, telecom and security. Especially mobile phones have driven that trend to todays ultra-small cameras embedded into the handset. While the image capture IC features ever-decreasing pixel geometries and surging megapixel numbers, the readout circuitry and optical systems are now challenged to follow-up with this trend. This paper describes a miniaturization approach using advanced packaging techniques for the electronic system (bare die assembly in stack-wirebond and flip chip) onto a high density circuit board and leveraging a MEMS based optical system providing the possibility for a variable focus lens and aperture concept. This can give rise to a camera including the optical system with just ~3 mm times 10 mm times 10 mm total dimensions. For prototypes, some electronic bare dice are mimicked by de-capsulating the IC from the plastic housing and re- bumping it for use as flip chip. This prototype procedure is also described. Operation of the MEMS device challenges the assembly technique for particulate free manufacturing of all back end processes. Bare die assembly with wirebond and flip chip provides ultimate miniaturization onto a rigid-flex multi layer PCB. The process flow for MOEMS assembly, electronic components assembly and final housing is designed to be generically applicable to current and future needs of ultraminiaturized cameras.

Building academic, research, and commercialization programs in micro and nano science and engineering at the University of Utah

This paper presents a case-study of some University/Government/Industry interactions at the University of Utah that build research and academic programs and create opportunities for economic growth in the areas of micro and nano science and engineering.