Fan Zeng

Improved Designs for an Electrothermal In-Plane Microactuator

Reported presently are two design approaches to improve the performance of an electrothermal in-plane microactuator with “chevron” beams. One incorporates beams with uniform cross sections but nonuniform lengths or tilt angles to accommodate the thermally induced expansion of the “shuttle”; the other incorporates beams with nonuniform cross sections to widen the high-temperature “expansion” zones. It is derived analytically, verified using finite-element simulations, and tested by microfabricating actuators occupying a constrained device area that the incorporation of one or the other proposed features leads to an improved performance figure-of-merit, defined to be the product of the actuation displacement and force. An increase in the figure-of-merit by up to 65% per beam has been measured.

Self-formed cylindrical microcapillaries through surface migration of silicon and their application to single-cell analysis

Surface migration of monocrystalline silicon has been applied to demonstrate self-formed cylindrical microcapillaries with diameters from 0.8 to 2.8 μm based on the microstructured substrate topography. The microcapillaries are entirely enclosed in silicon and can be conveniently etched to create fluidic access ports and microchannels for their subsequent integration into functional microfluidic devices. Moreover, the microcapillaries can be thermally oxidized through their access ports with silica walls remain intact upon release from surrounding silicon in an effort to enhance optical clarity. Straight microcapillaries and microcapillaries with perpendicular turns and crossings (junctions) have all been fabricated and validated for fluidic continuity with a fluorescein solution pumped through. The utility of the microcapillaries has been showcased on particle traps in which biological cells are probed for single-cell impedance spectroscopy. The approach disclosed, given its full compatibility with semiconductor device fabrication, offers great potential towards intelligent cell and molecule-based devices merging microelectronics and microfluidics. (Some figures may appear in colour only in the online journal)

A technology for monolithic MEMS-CMOS integration and its application to the realization of an active-matrix tactile sensor

Presently described is an application of a technology based on the surface-migration of silicon for the monolithic integration of micro-mechanical devices and complementary metal-oxide-semiconductor (CMOS) electronic circuits. A cavity sealed with a cover-diaphragm is first formed without a sacrificial layer etch. The electronic devices are next fabricated. The issues of material- and process-incompatibility inherently present in many integration schemes are largely avoided. A 16×16 active-matrix tactile sensor integrating 256 force-sensing diaphragms, 512 pixel transistors and 512 piezoresistors was designed, realized and characterized. The spatial resolution of the sensor was ~145 “pixels per inch” and the pressure sensitivity was ~0.07 μV/V/Pa.

Designs for improving the performance of an electro-thermal in-plane actuator

Reported presently are two designs to improve the performance of a “chevron” electro-thermal in-plane actuator. One incorporates beams with uniform cross-sections but nonuniform lengths and tilt angles to accommodate the thermally induced expansion of the “shuttle”; the other incorporates beams with non-uniform cross-sections to achieve a wider spread of the high temperature “expansion” regions of the beams. With the product of the actuation force and displacement defined as a figure-of-merit, it is verified using finite-element simulation that the incorporation of non-uniform lengths and tilt angles, and non-uniform beam cross-sections leads to respective improvement of 10 and 65% in the figure-of-merit. The effectiveness of these designs was also tested by micro-fabricating actuators occupying fixed device areas.

MEMS pressure sensors for high-temperature high-pressure downhole applications

This paper outlines the approach to realize a MEMS pressure sensor suitable for meeting the stringent requirements of sensing in a downhole environment reaching 175-oC temperature and 200-MPa pressure while maintaining an accuracy of better than 0.02% for an extended measurement period of several weeks during oil and gas exploration. A few sensing structures are proposed and strategies for their optimization are discussed for this unique application.

A Self-Scanned Active-Matrix Tactile Sensor Realized Using Silicon-Migration Technology

A process based on the silicon-migration technology for the monolithic integration of micromechanical devices and complementary metal-oxide-semiconductor (CMOS) circuits is described. A cavity sealed with a silicon cover-diaphragm is first formed without the need of a sacrificial layer etch. The transistors are next fabricated. The issues of material and process incompatibility inherently present in many schemes of microsystem integration are largely avoided using this technique. The technology was demonstrated with the design, fabrication, and characterization of a 16 × 16 active-matrix tactile sensor integrated with a 16-stage CMOS ring counter for row scanning.

Silicon-migration technology for MEMS-CMOS monolithic integration

A scheme for the monolithic integration of complementary metal-oxide-semiconductor (CMOS) circuits and microelectromechanical systems (MEMS) based on the silicon-migration technology (SiMiT) is developed. The process-incompatibility issues inherently present in traditional integration schemes are largely avoided by the elimination of the sacrificial layer etch. This pre-CMOS integration scheme is demonstrated using a 16×16 active-matrix tactile sensor “addressed” with an integrated ring counter.