Kristofer S. J. Pister

Micromachined free-space integrated micro-optics

Abstract The surface-micromachining technique has been employed to fabricate novel three-dimensional micro-optical elements for free-space integrated optics. The optical axes of these optical elements are parallel to the substrate, which enables the entire free-space optical system to be integrated on a single substrate. Microscale Fresnel lenses, mirrors, beam splitters, gratings, and precision optical mounts have been successfully fabricated and characterized. In addition, micropositioners such as rotary stages and linear translational stages are monolithically integrated with the optical components using the same surface-micromachining process to provide on-chip optical alignment or optomechanical switching. Self-aligned hybrid integration with semiconductor edge-emitting lasers and vertical cavity surface-emitting lasers are also demonstrated for the first time. This new free-space micro-optical bench (FSMOB) technology could significantly reduce the size, weight, and cost of most optical systems, and could have a significant impact on optical switching, optical sensing and optical data-storage systems as well as on the packaging of optoelectronic components.

Surface-micromachined components for articulated microrobots

A class of articulated micromanipulator robots with multiple degrees of freedom, workspaces on the order of a cubic millimeter, and payloads on the order of a milligram are proposed. Rigid links, mechanical couplings, and large-force, large-displacement micromotors have been created. Hollow triangular beams made from rotated microhinged polysilicon plates with polysilicon locks can withstand axial loads of up to 2.6 gm. Mechanical couplings with sliding mechanisms are used to rotate hinged structures off the substrate. The typical frictional force observed is approximately 2 /spl mu/N. Linear electrostatic stepper motors with an estimated force of 6.5 /spl mu/N at 35 V and a travel of 40 /spl mu/m have also been demonstrated.

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.

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.

Micromachined corner cube reflectors as a communication link

This paper proposes using a micromachined corner cube reflector to transmit data digitally by modulating reflected light intensity. Corner cube reflectors ranging in size from 100 to 200 μm have been built using hinged polysilicon plates. The reflectivity of polysilicon has been measured to be 24% and the total reflected power from the corner cube has been measured to be between 1 to 2% of the incident power. Orthogonality between plates is within roughly 8 mrad. Reflection from individual polysilicon plates has been modulated using electrostatic actuation with an applied voltage as low as 8 V.

Micromachined integrated optics for free-space interconnections

A novel surface micro-machined micro-optical bench (MOB) has been demonstrated. Free-space micro-optics such as micro-Fresnel lenses, rotatable mirrors, beam-splitters and gratings are implemented on a single Si chip using IC-like microfabrication processes. Self-aligned hybrid integration with semiconductor lasers are also demonstrated for the first time. The MOB technology realizes a microoptical system on a single Si chip and has significant impact on free-space integrated optics, optical switching, optical data storage, and optoelectronic packaging. free-space. Using this new technique, threedimensional micro-optical components can be fabricated integrally on a single Si chip. The Si substrate serves as a “micro-optical bench (MOB)” on which micro-lenses, mirrors, gratings and other optical components are pre-aligned in the mask layout stage using computer-aided design and then constructed by microfabrication. Additional fine adjustment can be achieved by the on-chip micro-actuators and micropositioners such as rotational and translational stages. With hybrid integration of active optical devices, a complete optical system can be constructed on the MOB, as illustrated in Fig. 1.

Standard CMOS piezoresistive sensor to quantify heart cell contractile forces

A MEMS force transducer system, with a volume less than one cubic millimeter, is being developed to measure forces generated by living, isolated cardiac muscle cells. Cell attachment and measurement of contractile forces have been demonstrated with prototype hinged polysilicon devices. A new transducer system has been fabricated using a standard CMOS process with a post-processing XeF/sub 2/ etch step. The system consists of a three dimensional oxide structure with aluminum hinges, polysilicon piezoresistive sensor, and CMOS amplifier. System response is 0.45 mV//spl mu/N. This MEMS force transducer will permit improved resolution of the mechanisms of muscle contraction.

Microelectromechanical Components For Articulated Microrobots

We propose to create a class of articulated micromanipulator robots with multiple degrees of freedom, workspaces on the order of a cubic millimeter, and payloads on the order of a milligram. We have created rigid links, mechanical couplings, and large-force, large-displacement micromotors. Hollow triangular beams made from rotated microhinged polysilicon plates can withstand axial loads of up to 2.3 gm. Mechanical couplings are used to rotate folded structures off the substrate with less than 2μN of force. Linear electrostatic stepper motors with an estimated force of 6.5μN at 35V and a travel of 40μm have also been demonstrated.

Self‐aligned hybrid integration of semiconductor lasers with micromachined micro‐optics for optoelectronic packaging

Novel self‐aligned hybrid integration of semiconductor lasers with three‐dimensional micro‐optical components has been demonstrated. The self‐alignment structures are fabricated integrally with other three‐dimensional micro‐optical elements such as micro‐Fresnel lenses, mirrors, and gratings on a single Si chip by surface micromachining technology. The Si substrate serves as a free‐space micro‐optical bench for active and passive optoelectronic components. A divergent beam emitted from an edge‐emitting semiconductor laser has been successfully collimated by the integrated micro‐Fresnel lens. The integration scheme offers a new approach for optoelectronic packaging and a new technology platform for integrating complete free‐space micro‐optical system on a single chip.

Parameterized layout synthesis, extraction, and SPICE simulation for MEMS

A suite of software tools which implements parameterized layout synthesis and SPICE simulation for surface-micromachined micro-electrical-mechanical systems (MEMS) is presented. These tools and techniques are demonstrated by using the design of a MEMS linear resonator as an example, and the various stages of this design are examined, including the generation of the circuit layout from performance specifications, the simulation of the devices, and the testing of actual fabricated resonators.