- •Brian Carl Morgan, Doctor of Philosophy, 2006
- •1. Introduction
- •Introduction
- •Passive Techniques
- •Active Techniques
- •Thesis Objectives and Structure
- •Chapter 2: gray-scale technology
- •Introduction
- •Gray-scale Background
- •Theoretical Background
- •Optical Mask Constraints
- •Standard Lithography Process
- •Design and Lithography Advancements
- •Minimum Feature Limitations
- •2.3.3. Double Exposures
- •Pattern Transfer
- •Deep Reactive Ion Etching (drie)
- •Selectivity Characterizations
- •Technology Collaborations
- •Phase Fresnel Lens (nasa)
- •2.5.2.1. Compensated Aspect Ratio Dependent Etching (carde)
- •Conclusion
- •Chapter 3: elect rostatic comb-drives using goay-scale technology
- •Introduction
- •Electrostatic Actuation Fundamentals
- •Tailored Comb-finger Design and Simulation
- •Analytical Displacement Simulations (2-d)
- •Finite Element Analysis (3-d)
- •Instability Considerations
- •Reduced Height Suspensions
- •Fabrication
- •Comb-drive Testing
- •Reduced Height Comb-fingers
- •Conclusion
- •Introduction
- •Tunable mems Resonator Operation
- •1. Introduction 1
- •1.1. Introduction 1
- •2.1. Introduction 11
- •3.1. Introduction 36
- •4.1. Introduction 51
- •Gray-scale Electrostatic Springs
- •Testing and Characterization
- •Conclusion
- •Introduction
- •Device Concept
- •Figure 5.5: Calculated coupling as two co-axial single-mode fibers are separated longitudinally.
- •Figure 5.6: Alignment schematic for a bent fiber cantilever coupling to a fixed output fiber.
- •Alignment Wedges
- •Fabrication
- •Assembly
- •Actuation Concept Demonstration
- •Introduction
- •Experimental Setup
- •Static Testing
- •Table 6.3: Measured fiber locations for discrete actuation voltages. These 4 points form the corners of a diamond shaped alignment area.
- •Channel a (va2)
- •1. Introduction 1
- •1.1. Introduction 1
- •2.1. Introduction 11
- •3.1. Introduction 36
- •4.1. Introduction 51
- •Horizontal displacement
- •Voltage Squared (v2)
- •Auto-alignment Algorithms
- •Figure 6.16: Simplified hill-climbing algorithm block diagram.
- •Automated Fiber Alignment Results
- •Settling Time, Coarse Threshold Power (%Peak)
- •Testing Summary and Discussion
- •Conclusion
- •Summary of Accomplishments
- •Future Work
Summary of Accomplishments
This PhD dissertation has investigated electrostatic MEMS actuators incorporating 3-D features fabricated with gray-scale technology. While traditional MEMS actuators have been limited to planar design and fabrication, the integration of 3-D components has enabled improved performance and increased (or otherwise impossible) functionality. This research is the first to demonstrate such a beneficial marriage between MEMS actuators and a batch 3-D fabrication technique. Developed devices include static 3-D comb-drives, tunable MEMS resonators, and a novel 2-axis fiber alignment device.
The specific accomplishments of this PhD dissertation are as follows:
Gray-scale Technology Development: Complex 3-D photoresist and silicon profiles were controlled through a developed empirical model of the gray-scale lithography process and extensive DRIE pattern transfer characterization. A double-exposure technique was demonstrated as a method to exponentially increase the vertical resolution of 3-D structures, while the CARDE process was introduced as an effective technique for anticipating aspect ratio limitations during DRIE. Static applications of gray-scale technology were demonstrated through three technology collaborations: (a) Development of a variable span microcompressor (U.S. Army Research Laboratory and Massachusetts Institute of Technology); (b) Design and fabrication of 3-D substrates for a MOSFET relay package (Toshiba Corporation); (c) Design, fabrication, and testing of x-ray phase Fresnel lenses (NASA-Goddard Space Flight Center).
Compact Tailored Electrostatic MEMS Comb-drives: Variable height grayscale structures were integrated with electrostatic MEMS actuators for the first time. Analytical and FEA methods were developed to model comb-drives with variable height comb-fingers, enabling tailored displacement characteristics without increasing device area. Local reduction of actuator suspension height enabled dramatic (70%) reductions in spring constant, leading to lower driving voltages. The design and fabrication techniques developed to integrate gray-scale technology within an electrostatic MEMS actuator process flow serves as a platform for developing more complex 3-D shaped actuators.
Vertically-Shaped Tunable MEMS Resonators: Research on vertically shaped comb-drive actuators was extended to create new compact tunable MEMS resonators. Voltage-controlled electrostatic springs were designed, modeled, and fabricated; capable of bi-directional resonant frequency tuning of in-plane comb resonators. Simulations showed that multi-step comb-finger profiles or variable- engagement comb-finger designs can be used to minimize non-linear stiffness coefficients during large amplitude resonator oscillations. MEMS resonators in the low kHz range demonstrated electrostatic springs as strong as 1.19 N/m (@70V) and enabled tuning of the resonant frequency by up to 17.1%.
Gray-scale Fiber Aligner: A novel 2-axis optical fiber alignment system using 3-D wedges (fabricated with gray-scale technology) was created for the first time. Without the integration of these 3-D components, this new class of actuators would be otherwise impossible or impractical. Devices were designed, fabricated and tested based on experience with comb-drive actuators and gray-scale integration.
Auto-alignment algorithms were developed and implemented to demonstrate the ability of final devices to align an optical fiber to a specific target, with particular emphasis on comparing overall alignment time and achievable resolution. Methods for Cartesian control and evaluating hysteresis of these actuators were also developed. Device switching speeds were measured to be consistently <1ms, while alignment times of <10sec to a fixed 2p,m square indium phosphide (InP) waveguide with <1.6p,m resolution were commonly achieved. Ultimately, grayscale fiber aligners were able to achieve alignment ranges as large as 40p,m (at fiber tip) in both the in-plane and out-of-plane directions, with alignment resolution of <1.25p,m. These results represent a significant step towards cost effective inpackage fiber alignment in optoelectronic packaging.