David A. Winick

MEMS-based diffractive optical-beam-steering technology

This paper presents some results from phase-1 research into developing a beam steerer based on micro-mechanical diffractive elements. The position of these elements is electrostatically controlled, to allow dynamic programming of a 2D phase function. Feasibility prototypes were constructed in the MUMPs polysilicon surface micromachine process.

Design of rotating MEMS tunable capacitors for use at rf and microwave frequencies

With the recent surge in popularity of RF and Microwave MEMS many different device topologies are being explored. Some devices provide large changes in capacitance, but lack the ability to provide a linear range of capacitance values between the minimum and maximum values of the device. We present a device design for a low-loss rotating MEMS tunable capacitor that once programmed to the required value consumes no power. This device design is transformed from gear structures currently designed in the SUMMiT process with modifications made so that the device may be used as a varactor. Modifications include alterations of physical structure, drive mechanism for programming capacitance value, and additional post processing steps needed to provide low-loss at RF and Microwave frequencies. Many different device structures are possible each with performance, potential reliability, and potential yield trade offs that must be considered. Post processing is required to add metal to provide sufficiently low loss for high quality components. Since device planarity is critical for operation, a novel post-process metal deposition technique for providing low stress metal was concieved. Additional modifications to compensate for polysilicon warpage are considered for future investigation. Simulation results based on high frequency full wave analysis software show a highly linear tuning range and a capacitance ratio approaching 6 to 1. A model is extracted from the scattering parameters provided by HFSS and then various device sizes and topologies are compared.

MEMS-based capacitor arrays for programmable interconnect and RF applications

We describe a programmable capacitor technology under development at NCSU and its potential application in building programmable interconnect devices useful for system level connectivity functions, phased array beam steering and RF switching. Crossbars are made from arrays of electrostatically controlled bistable MEMS-based capacitors. These new devices allow faster signaling and consume less power than BiCMOS (or even CMOS) crossbars. We describe the essential elements of these arrays and present results obtained so far.

Programmable MEMS capacitor arrays

We describe a programmable capacitor technology under development at NCSU and its potential application in building programmable interconnect devices useful for system level connectivity functions, phased array beam steering, and RF switching. Crossbars are made from arrays of electrostatically controlled bistable MEMS-based capacitors. These new devices allow faster signaling and consume less power than BiCMOS crossbars. They also allow critical RF components to be shrinked in size substantially. We describe the essential elements of these arrays and present results obtained so far.

A micro-machined approach to optical interconnect

This paper describes several innovative optical modulator devices for reconfigurable free-space interconnect, in an effort to demonstrate both the technology limitations and the performance advantages available via this application of microelectromechanical systems.

An integrated self-masking technique for providing low-loss metallized RF MEMS devices in a polysilicon only MEMS process (Invited Paper)

A novel masking technique that enables the complex patterning of metal on any layer of a released MEMS chip is demonstrated. This technique enables a polysilicon only MEMS process to create low-loss RF devices. To illustrate the advantages of post-release metallization, in a polysilicon only MEMS process, a rotating MEMS tunable capacitor that provides a wide and linear tuning range is presented. The core of the design comes from high yield, mechanically proven gear designs from Sandia’s SUMMiT design library. Significant alterations were made to the gear structure to create the final device. Preliminary tests show device capacitance ratios of 1.8:1, with linear tuning. Increased metal deposition to reduce the device air gap, can produce a capacitance ratio over 6:1.

Optomechanical variations and control in a MOEMS switch model

This work demonstrates how optomechanical alignment inaccuracies affect the operation of a small port-count, fiber coupled, MOEMS switch using six degrees of freedom, parameterized behavioral models. Simulation results show that a control system is essential to stabilize the switch when it is subjected to the variations that would otherwise degrade its performance.

Improving interconnect characteristics of thin film MEMS processes

One problem faced by designers utilizing polysilicon based surface micromaching processes is the poor conductivity of polysilicon. Process factors preclude inclusion of metal layers in these processes before the final polysilicon layer is annealed. Adding metal after anneal but before release restricts the metal to only the top layer of the design, making it much less useful for interconnect, and restricting reflective surfaces to the top layer. We present techniques for adding metal after release which avoid some of the usual pitfalls. Application areas for which these techniques could prove useful include RF, Microwave, Optical MEMS, and MEMS devices used in high-speed digital communications. Creating a multilayer metal interconnect is enabled by utilizing a self-masking approach to avoid shorting, and applying e-beam evaporation from a variety of angles. Using this approach, even lower level polysilicon lines can be metallized. Results using two deposition angle recipes on test structures and devices fabricated in a thin film MEMS process are presented.