Richard Yeh

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.

Dephosphorylation of tau during transient forebrain ischemia in the rat.

The effect of transient cerebral ischemia on phosphorylation of the microtubule-associated protein (MAP) tau was investigated using the rat four-vessel occlusion model. Phosphorylation of tau is proposed to regulate its binding to microtubules, influencing the dynamics of microtubule assembly necessary for axonal growth and neurite plasticity. In this study, tau was rapidly dephosphorylated during ischemia in the hippocampus, neocortex, and striatum. Dephosphorylation of tau was observed within 5 min of occlusion and increased after 15 min in all three brain regions, regardless of their relative vulnerability to the insult. Thus, dephosphorylation of tau is an early marker of ischemia and precedes the occlusion time required to cause extensive neuronal cell death in this model. On restoration of blood flow for a little as 15 min, tau was phosphorylated at a site(s) that causes a reduction in its electrophoretic mobility. The dephosphorylation/phosphorylation of tau may alter its distribution between axon and cell body, and affect its susceptibility to proteolysis. These changes would be expected to influence microtubule stability, possibly contributing to disruption of axonal transport, but also allowing neurite remodeling in a regenerative response.

Design of low-power silicon articulated microrobots

We are creating a class of autonomous low-power silicon articulated microrobots fabricated on a 1 cm2 silicon die and mounted with actuators, a controller, and a solar array. By taking advantage of the high force-density of electrostatic actuators in the micro scale, low-power actuators can be made for microrobots. A micromotor with an energy efficiency of 4%, that uses CMOS-compatible supply voltage, and has a motion resolution of 2 μm has been demonstrated in a volume of 0.015 mm3. Articulated two degrees-of-freedom legs with built-in mechanical couplings have been fabricated in a commercial micromachining foundry (MUMPs) and successfully assembled. Lowpower CMOS electronics will be used to control the robot locomotion and a solar array chip will be used to power the microrobot.

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.