Thorbjörn Ebefors

Three dimensional silicon triple-hot-wire anemometer based on polyimide joints

The first three dimensional (3D) flow sensor probe based on polyimide joints has been fabricated and successfully tested. The new 3D sensor, which is specially designed for turbulent gas flow measurements, is based on the anemometer principle, i.e. gas cooling of electrically heated hot-wires. The sensor probe consists of three perpendicular 500 /spl mu/m/spl times/5 /spl mu/m/spl times/2 /spl mu/m polysilicon hot-wires giving a measuring volume sufficiently small to resolve the small eddies in a turbulent flow. A bulk micromachining process in combination with sacrificial etching is used to form the hot-wire probes. The hot-wires are connected to 30 /spl mu/m thick bulk silicon beams which are defined by double sided KOH etching. Two wires (x and y) are located in the wafer plane and the third z-wire is rotated out of the plane using a new robust micro-joint. The self-assembly micro-joint with small bending radius is based on thermal shrinkage of polyimide in V-grooves. High flow sensitivity for the anemometric hot-wires has been measured. Time constants of 120 and 330 /spl mu/s were measured for the cooling and heating of the hot-wires, respectively.

New small radius joints based on thermal shrinkage of polyimide in V-grooves for robust self-assembly 3D microstructures

A novel and simple technology for making robust three-dimensional (3D) silicon structures with small radii of bending has been developed and investigated. The proposed self-assembly method of bending 3D structures out of plane such that they stay bent without any interlocking braces is based on thermal shrinkage of polyimide in V-grooves. A wide range of bending angles for the permanent out-of-plane rotated structure can be chosen by varying the curing temperature of the polyimide. The relatively large thermal expansion of polyimide makes it possible to use the structure in a dynamic mode useful for compensation of undesired process variations. The proposed technique is compatible with both IC based surface micromachining and batch fabrication. Therefore, structures based on the new polyimide joint have general applications in micromachining and can be used in many new 3D sensors or actuators having detailed features in all three dimensions. For the tested polyimide V-groove joints, static bending angles between and have been achieved with a maximum bending angle of per V-groove. Bending radii smaller than 60 m for a 30 m thick out-of-plane rotated silicon plate have been measured. Electrical connections to the assembled structures have been investigated. It has been shown that the aluminium conductors crossing the V-grooves in the polyimide joint are not affected by the out-of-plane rotation.

Dynamic actuation of polyimide V-groove joints by electrical heating

Abstract New robust three-dimensional silicon structures with integrated heaters for dynamic actuation have been fabricated and tested. The structures can be used in both static and dynamic modes for 3-D sensor and actuator applications. The proposed technique for bending 3-D structures out of the wafer plane is based on thermal shrinkage of polyimide in V-grooves, producing static bending. This static angle can be chosen in a wide range by varying the curing temperature. The relatively large thermal expansion of polyimide makes it possible to use the structure in dynamic mode. A local power dissipation in the joint is achieved by using a current through an integrated heater. This makes it possible to control the bending angle of each individual structure. For the tested polyimide V-groove joints, static bending angles of 35 ° and dynamic angles of 3 ° per V-groove have been achieved.

A robust micro conveyer realized by arrayed polyimide joint actuators

A new micro motion system (micro-conveyer) based on arrays of movable robust silicon legs has been developed and investigated. The motion is achieved by thermal actuation of polyimide joint actuators using electrical heating. Successful experiments on moving flat objects in the millimeter range with high load capacity have been performed. The conveyer consists of a 15/spl times/5 mm/sup 2/ chip with 12 silicon legs each 500 /spl mu/m long. The maximum load conveyed on the structure was 2000 mg. Conveyance velocities up to 12 mm/s have been measured. Accelerated lifetime measurements demonstrate the long-term stability of the actuators. The function of the polyimide joint actuators is unaffected after more than 2/spl times/10/sup 8/ load cycles.

New robust small radius joints based on thermal shrinkage of polyimide in V-grooves

A novel and simple technology for making robust three-dimensional (3-D) silicon structures with small radii of bending has been developed and investigated. The proposed method of bending 3-D structures out of plane so that they stay bent without special locking arrangements is based on thermal shrinkage of polyimide in V-grooves. The structures can be used in both static and dynamic mode for 3-D sensor or actuator applications.

Hybrid-mounted micromachined aluminum hotwires for wall shear-stress measurements

In this paper, we present a micromachined metal hotwire anemometer sensor for use in wall shear-stress measurements. We describe its design and fabrication. A novel hybrid assembly method has been developed to make it possible to measure close to the surface without contacting leads interfering with the flow. Experimental results illustrate the behavior and characteristics of this sensor.

Permeability Enhancement by Multilayer Ferromagnetic Composites for Magnetic-Core On-Chip Inductors

This letter reports about unpatterned ferromagnetic NiFe/AlN multilayer composites used as advanced magnetic core materials for on-chip and interposer integrated inductances. The proposed composite structure reduces RF induced currents and thus pushes the permeability cutoff to beyond 3.7 GHz, which is by a factor of 7.1 higher than for homogeneous NiFe layers of same thickness. To the best knowledge of the authors, we achieve the highest effective relative permeability of 28 at 1 GHz, highest ferromagnetic resonance frequency and highest inductance enhancement factor above 1 GHz ever reported for devices based on on-chip unpatterned NiFe magnetic cores. A single loop inductor is also implemented as a technology demonstrator, achieving an inductance enhancement of 4.8 and a quality factor enhancement of 4.5 at 400 MHz.

Design and Fabrication of Addressable Microfluidic Energy Storage MEMS Device

Design and fabrication of microfluidic energy storage devices that are based on the control of the liquid electrolyte inside a power cell are presented. A 12-cell array of individually addressable reserve microbatteries has been built and tested, yielding ~ 10-mAh capacity per each cell in the array. Lithium and manganese dioxide or carbon monofluoride (Li/MnO2 and Li/CFx) have been used as anode and cathode in the battery with LiClO4 -based electrolyte. Inherent power management capabilities allow for sequential single cell activation based on the external electronic trigger. The design is based on the superlyophobic porous membrane that keeps liquid electrolyte away from the solid electrode materials. When power is needed, battery activation (a single cell or several cells at once) is accomplished via electrowetting trigger that promotes electrolyte permeation through the porous membrane and wetting of the electrode stack, which combines the chemistry together to release stored electrochemical energy. The membrane and associated package elements are prepared using microelectromechanical system fabrication methods that are described in details along with the assembly methods.

Hybrid mounted micromachined aluminium hot-wire for near-wall turbulence measurements

We present the first micromachined metal hot-wire anemometer sensor for use in near-wall turbulence measurements. To measure close to the surface without the circuitry interfering with the flow, a novel hybrid assembly of the sensor has been developed. We present the design, fabrication and characteristics of this sensor.

Multilayer ferromagnetic composites enabling on-chip magnetic-core inductors beyond 1 GHZ

This paper reports of fabricated unpatterned ferromagnetic NiFe/AlN multilayer composites and an established process flow for magnetic core material suitable for integration with Silex 3D RF TSV technology. The fabricated single-loop test inductors achieved an inductance enhancement of 4.8 and a quality factor enhancement of 4.5 at 400 MHz. Simulations show that magnetic material in connection with 3D TSV inductors result in an inductance enhancement up to a factor of 5 at GHz frequencies for the same inductor area or the same inductance can be achieved at 9 times smaller area and cost.