Stephanus Buettgenbach

Centering electrostatic microgripper and magazines for microassembly tasks

Accurate handling of microparts is one of the major tasks for an automated microproduction. The development of centering electrostatic handling devices is described. Based on a planar design common microtechnical fabrication methods were used. Therefore the gripper electrodes can easily be miniaturized and the geometric form can be adapted to the shape of the objects to be handled. The optimization of the design of the gripper was done by using the Finite Element Method. This gave the possibility to improve the centering effect and the gripping forces without increasing the operating voltage. To enable the observation of the gripped parts with a camera, a transparent substrate was used (Pyrex-wafer). This facilitates the integration of the gripper into a sensor controlled microassembly station. Futhermore first successful tests of functional models are described.

Novel fabrication process for 3D meander-shaped microcoils in SU-8 dielectric and their application to linear micromotors

This paper reports on an optimized fabrication process for three dimensional coil structures such as meander or helical coils wound around in plane magnetic structures. The process consists of UV depth lithography employing AZ4562 and SU8 photo resists and electroplating of copper and nickel-iron. Furthermore SU8 is used as the embedding dielectric due to its excellent planarization properties and high structural aspect ratio. Special emphasis was laid on the decrease of via interconnect resistance by electroplating the vias and upper conductors in a single step thus avoiding a large number of resistive interfaces. This was achieved by sacrificial wiring and structured seed layers. The developed technology is applied to a variable reluctance micro motor with a novel design that avoids high friction. The presented concept makes use of a stator traveler configuration generating complementary attraction forces. The technology and design concept is presented and first results are demonstrated.

Fabrication of thin film resistors and silicon microstructures using a frequency-doubled Nd:YAG laser

A laser-assisted technology for the fabrication of micro electro mechanical system has been developed. This method allows micromachining of bulk silicon wafers and silicon membranes by using a Q-switched Nd:YAG-laser with optional frequency doubling. Moreover, thin gold film resistors can be patterned on passivated silicon and glass substrates. Because direct laser processing is a highly flexible and timesaving method it is well studied for rapid prototyping and small volume production. Combining laser micromachining with conventional photolithographic techniques new designs of microsensors and actuators can be achieved.

Novel three-axis silicon probe with integrated circuit on chip for microsystem components

A three-axis micro probe with wiring of the piezoresistors to Wheatstone bridges on the silicon membrane was currently developed for application in high precision coordinate measuring machines (CMM). The methods and results of the experimental investigation of the main properties of the 3d micro probe are presented. The influence of temperature and light onto the probe performance is described. Finally a brief outlook on the optimization of the threshold sensitivity is given.

New pneumatically actuated miniature gripper for microassembly

This paper presents a micro gripper driven by a new piston type pneumatic micro actuator. The basic structure of the micro gripper and the actuator are fabricated by silicon dry etching in a single etch step. The device consists of a pyrex-silicon-pyrex sandwich structure which was mounted by anodic bonding. Alternatively a SU8 depth lithography process was used to realise the pneumatic driven micro gripper. The assembly of various micro parts including a recently presented tactile silicon 3D-micro probe is described.

Computational synthesis of lithographic mask layouts for silicon microcomponents

In order to efficiently design complex micromechanical systems there is a growing demand for layout synthesis tools that directly derive the layout description from the device description. This paper outlines a systematic method of using genetic algorithms to synthesize the lithographic mask layout of micromachined silicon devices. The procedure has been implemented in the computer program OMEA, which calculates an optimal or semi-optimal layout description from the three-dimensional device description of the component. Currently, this method is applied to chemical deep etching of silicon. To model the structuring process the program makes use of a coupled etch simulator. Synthesis results show that the design engineer is enabled to take full advantage of the possible design space of the underlying process technology. The tool is an integrated part of the CAD environment BICEPS. In order to demonstrate the capability of the concept the design process of a spring actuator is described in detail.

Silicon three-axial tactile probe for the mechanical characterization of microgrippers

A three-axial tactile micro probe for the investigation of the mechanical behavior of micro grippers and other micro assembly equipment has been developed using silicon micromachining technology. The sensor has been used to measure the restoring forces of flexural hinges in a micro gripper gear, to calibrate an integrated gripping force sensor, and to measure the generated forces of actuators used in micro grippers. The tactile micro probe is an advancement of a 3-D force sensor presented earlier.

Tolerance analysis and synthesis in microsystems

The large variety of the technologies and physical, chemical or biochemical effects united in micro systems requires a new generation of quality assurance. An appropriate quality management should check all conceivable influences on the product and perform a complete tolerance synthesis based on its function and with regard to manufacturing and cost optimization. In the following, a new approach to function-oriented tolerance analysis and synthesis is presented. The Institutes for Engineering Design and Micro Technology in Braunschweig, Germany, have developed a computer program, which assists Design Engineers in tolerance analysis and synthesis in micro technology. This contribution presents the theoretical background of this software. For a better understanding two short MEMS examples are shown.

New differential-type SMA actuator for a miniature silicon gripper

This paper presents two new designs for a differential-type SMA actuator for a silicon micro gripper. The basic structure of the micro gripper is fabricated by silicon dry etching. The SMA actuators have been realized by machining a NiTi foil with a thickness of 50 ?m. It has been cut by direct laserwriting using a Q-switched Nd:YAG-laser followed by a wet chemical etch step to remove the heat affected zone (HAT). The first design is an advance of a recently presented actuation system with an optimized configuration of the SMA actuator. A critical aspect is the high force necessary to imply the low temperature shape of the inactive actuator which has to be transmitted by the gripper gear. This problem has been overcome by the second design where these high forces are transmitted directly between the active and the inactive actuator of the differential-type actuator. Tests of this new actuator and a new gipper design modified to meet the requirements of the actuator are described.

Silicon microgripper for microassembly realized by photolithography and fast anisotropic silicon etching

In this paper we present a new silicon microgripper for microassembly realized by photolithography and fast anisotropic silicon etching. Technological and manufacturing problems of the silicon microgripper will be described. The optimized etch process results in a high silicon etch rate of up to 6.2 micrometers /min, a good selectivity silicon/photoresist of up to 100:1, a high anisotropy, a nearly vertical etch profile, and a smooth surface topography. Excellent profile control for trench etching with a depth of about 250 micrometers and an anisotropy of better than 0.98 at a mean etch rate of 4 micrometers /min was obtained. Higher etch rates of up to 6.2 micrometers /min have been achieved resulting, however, in lower anisotropy. The developed microgripper is driven by a differential-type shape memory alloy (SMA) actuator. SMA actuators exhibit the best power- to-volume ratio of all actuators, do not release any particles, and can perform various movements like bending, elongation or twisting. Heating can easily be achieved by direct electrical current. Therefore SMA actuators are well suited for microgripper applications.