Patrick B. Chu

Gas-phase silicon micromachining with xenon difluoride

Xenon difluoride is a gas phase, room temperature, isotropic silicon etchant with extremely high selectivity to many materials commonly used in microelectromechancial systems, including photoresists, aluminum, and silicon dioxide. Using a simple vacuum system, the effects of etch aperture and loading were explored for etches between 10 and 200 micrometers . Etch rates as high as 40 micrometers /minute were observed. Initial characteriation of wafer surface temperature during the etch indicates tens of degrees of self-heating, which is known to cause substantial decrease in etch rate.

Optical communication using micro corner cube reflectors

Surface micromachined corner cube reflectors made of 250 /spl mu/m square hinged polysilicon plates have been demonstrated to transmit digital signals over a range of 2 meters by reflecting an interrogating 5 mW laser. Measured reflectance ranges from 34% to 77% for different mirror designs. Divergence of light reflected by CCR ranges from 15-35 mrad. The CCRs are electrostatically actuated with 10 to 20 V. The highest data rate transmitted with a CCR is 1 Kbps.

Dynamics of polysilicon parallel-plate electrostatic actuators

Abstract The response of a polysilicon parallel-plate electrostatic actuator to a.c. signals at different bias voltages has been measured with a laser interferometer. Using microhinges, large plates (with areas from 100 μm2 to ≃ 0.1 mm2) with long thin support beams (such as 600 μm × 3 μm × 1.5 μm) are rotated off the surface of the substrate to form a parallel-plate capacitor. Fabricated structures having 100 μm gaps can be closed electrostatically with voltages as low as 50 V. This new actuator is estimated to output a force of up to 50 μN. With the exception of the resonant Q-value, the experimental results are in good agreement with simulations based on a simple nonlinear model for the actuator.

Electrostatic actuation of three-dimensional MEMS mirrors using sidewall electrodes

We propose and demonstrate electrostatic sidewall-electrodes actuation of three-dimensional (3-D) microelectromechanical systems (MEMS) gimbal mirrors. The linearity of the mirror angle dependence on actuation voltage is improved with the sidewall-electrodes actuation. In addition, the undesired spring-softening effect commonly found in electrostatic actuation, where the mirror resonance frequency decreases with increased tilt angle, is significantly reduced. Sidewall actuation enables superior performance of 3-D MEMS mirrors including large pull-in angles, reduced actuation voltages, improved device reliability, and fast switching times.

Optical methods for characterization of MEMS device motion

Micro-electromechanical system (MEMS) devices are small compared to normal mechanical devices, but they are still large compared to the wavelength of visible light. Thus, simple low- cost optical measurement techniques can be adapted for precise characterization of the motions of these small objects. The results of such measurements are important for verification of simulations, especially for devices in which nonlinear effects such as squeeze film damping play a significant role. The advantages and challenges of optical metrology for MEMS are examined using an electrostatically-actuated microgripper structure as an example device. Interferometric measurements of static rotation and of small-signal sinusoidal and impulse responses are presented.

MOEMS - Enabling technologies for large optical cross-connects

Rapid growth in demand for optical network capacity and the sudden maturation of wavelength-division-multiplexing (WDM) technologies have led to development of long-haul optical network systems that transport tens to hundreds of wavelengths per fiber, with each wavelength modulated at 10Gb/s or more. Micro-optical-electromechanical systems (MOEMS) devices, such as mirrors and lenses, are found to be the enabling technologies to build the next-generation cost-effective and reliable large port-count optical cross-connects (OXCs). While the basic roles of these MOEMS devices in an optical cross-connect are easily understood, the detailed mechanical design, electronics integration, packaging, control, and usage of these devices must reflect the stringent system requirements of the optical design and the electronic hardware of the network switch element. Due to the inter-dependence of many design parameters, manufacturing tolerances, and performance requirements, careful tradeoffs must be made to create reliable and manufacturable MOEMS devices. We describe various design tradeoffs and multi-disciplinary system considerations for building MOEMS-based large OXCs.

MEMS for optical communication: present and future

The current fiber optical communication system has evolved into a complicated multi-wavelength system with the deployment of Wavelength Division Multiplexing (WDM) networks. Many innovative technologies are desired to materialize its vast capacities and promises. MEMS technology has recently emerged as a competitive candidate to solve many technical challenges encountered in current WDM networks. Its applications have spanned from large scale optical switch fabrics such as optical cross-connects, optical add/drop multiplexers, to a large variety of active and passive optical components for transmission networks, such as tunable lasers and filters, dispersion compensation devices, amplifier gain equalizers, polarization controllers, and many others. In this paper we will discuss the current development status, promises and challenges, and the future prospects of MEMS technologies for optical communication, with a primary focus on MEMS-based optical cross-connects.

Optical communication link using micromachined corner cube reflector

An optical communication link using a micromachined corner cube reflector (CCR) was demonstrated to transmit digital signals over a range of 2 meters by reflecting an interrogating laser from a 5mW laser source. The surface micromachined CCRs are made of 250micrometers square hinged polysilicon plates and have measured reflectance ranging from 34 percent to 77 percent for different mirror designs. LIght reflected by the CCRs has a divergence ranging from 15-35mrad. The CCRs are electrostatically actuated with 10 to 20V. The highest data rate transmitted with a CCR is 1K bps. Theoretical analysis and some dynamic optical test results of the device are presented.