See-Ho Tsang

Control of the out-of-plane curvature in SU-8 compliant microstructures by exposure dose and baking times

The effect of processing conditions on the curvature of SU-8 cantilevers up to 6400 µm long is determined by experimental methods. Our observations suggest that a zero curvature condition can be achieved by controlling the exposure dose and post-exposure baking time for any given SU-8 thickness. The curvature of SU-8 cantilevers processed with different exposure doses and post-exposure baking times has been measured and reveals that the gradient of crosslinking density throughout the SU-8 film is the cause of out-of-plane stress. A general model for the SU-8 cantilever curvature is developed which explains the behavior of SU-8 structures that have been processed with different conditions and can be used to predict the general effect on the SU-8 cantilever curvature for different SU-8 thicknesses and process parameters.

Automated assembly of hingeless 90° out-of-plane microstructures

A novel design for hingeless out-of-plane microstructures is presented. These structures can be assembled to 90° by a single-point actuation, which can be provided by, for example, a microelectronics wirebonder or a microprober station. Both wirebonders and microprober stations are commonly available to microfabrication facilities, and therefore the assembly method described here introduces a practical and economical approach to the creation of out-of-plane structures. The microstructure designs can be used in many types of microfabrication processes, and in particular have been fabricated using both PolyMUMPs and an SU-8 technology developed at Simon Fraser University. In addition to the fabricated devices, we will present the results of finite element analysis (FEA). Also reported here are tests for positional repeatability and reliability.

Monolithically fabricated polymermems 3-axis thermal accelerometers designed for automated wirebonder assembly

This paper reports on two novel 3-axis thermal accelerometers based on different mechanical structures that are fabricated using polyimide PI-2611, and assembled using a standard wire-bonder. One accelerometer design has an un-amplified linear DC sensitivity of plusmn45 muV/g, plusmn60 muV/g, and plusmn35 muV/g on the X, Y, and Z axes respectively. The second design has a sensitivity of plusmn17 muV/g, plusmn8.5 muV/g, and plusmn14 muV/g respectively. Both accelerometers are assembled by applying a lateral push to each of the out-of-plane parts using an unmodified wire-bonder. This paper will detail the fabrication, design, assembly, and functional results of the two 3-axis thermal accelerometer designs.

Polydimethylglutarimide (PMGI) as a structural material for surface micromachining

This work investigates the use of polydimethylglutarimide, or PMGI, as a structural material for surface micromachining. PMGI is a commercially available, positive-toned deep-UV resist designed for use in bi-layer lift-off techniques. This paper presents a technique for the microfabrication of free-standing PMGI structures, and uses those structures to extract the coefficient of thermal expansion and Youngs modulus for PMGI. Our study found PMGIs coefficient of thermal expansion to be 56 ± 6 ppm °C−1 and Youngs modulus to be 5.0 ± 0.5 GPa. Active structures were also fabricated by including a patterned metal layer. This allows the fabrication of active devices, such as bent-beam actuators. PMGI is a commercially available polymer being used in micromachining, and this paper provides the first report of its thermo-mechanical properties.

Out-of-plane electrothermal actuators in silicon-on-insulator technology

A novel electrothermal micro-actuator capable of actuation after being rotated 90 out of plane is presented. The actuator is fabricated and characterized using the Micragem silicon-on-insulator (SOI) process developed by Micralyne Inc. The actuator is designed to be rotated out of plane by means of a serpentine spring design that provides electrical contact to the substrate while applying a downward force to hold the actuator in place. The eventual purpose of this actuator is to adjust the position of a micromirror at a 90 angle to the substrate. The actuator performs as expected in the horizontal position and can be assembled using standard microprobes. The actuator performance and the theory of spring operation are presented using an analytical heat transfer model, finite element modelling, and device measurements.

Spin-On Glass as a Sacrificial Layer for Patterned Metallization of Compliant SU-8 Microstructures

A new micromachining technique is described in this paper for polymer MEMS process. By using spin-on glass (SOG) as the underlying sacrificial layer, existing SU-8 micromachining processing has been enhanced to allow for metallization, patterning, as well as post-development hard baking of SU-8 structures. Chemical compatibility of the SOG sacrificial layer makes direct metallization and patterning on top of unreleased SU-8 structures possible. Detail fabrication process flow and fabricated structures are presented in this paper.

Exposure and development of thick polydimethylglutarimide films for MEMS applications using 254-nm irradiation

Polydimethylglutarimide PMGI-based resists are finding increasing use in microelectromechanical systems MEMS as both sacrificial and structural materials. PMGI-based resists are commercially available and were originally designed for use in bilayer lift-off applications. Literature on deep-UV exposure and development of PMGI films is limited to films less than 2.5 m in thickness, and use only tetramethylammonium hydroxide TMAH-based developers. We investigate the exposure and development of PMGI films greater than 6 m in thickness using the two main classes of developer for PMGI, TMAH, and tetraethylammonium hydroxide TEAH-based developers. At these thicknesses, a nonuniform dose through the film due to the optical absorption of the PMGI leads to large gradients in the dissolution properties. We report etch rates as a function of surface dose and development time. Additionally a model is developed to provide a basic predictor of development depth and other important data for fabrication process planning and development.

Fabrication of an inexpensive cleanroom module for microsystem testing

We have built a freestanding cleanroom module for microsystem testing. The environment has an interior floor space of 4.3 m × 2.1 m and a ceiling of 2.4 m (8 feet). The cleanroom module can be operated as a class 10 000 environment, and the cost of materials was less than CDN

Self-locking vertical operation single crystal silicon micromirrors using silicon-on-insulator technology

1900. In this paper, we describe the construction and testing of our cleanroom module.

Polymethylglutarimide As a Structural MEMS Material

Micro-opto-electro-mechanical systems (MOEMS) have been developed for a broad range of applications including: optical switching, optical data storage, imaging, bar code reading and beam steering for free-space optical communications. One vital component of these systems, the out-of-plane micromirror, is required for any redirection of light. The challenge for the design of these mirrors is to create an optically smooth and flat surface for producing minimum distortion reflections. If a micromirror scatters a significant amount of energy, then a higher power light source will be required reducing the efficiency and increasing the cost of the system. Typically, micromirrors fabricated through polycrystalline processes offer structural designs of multiple layers allowing for hinges to be created for out-of-plane operation. However, polycrystalline mirrors do not offer the flatness and smoothness that is achievable with single crystalline materials. Micromirrors made from single crystalline processes provide superior optical properties, but the complexity for designing out-of-plane structures is increased due to the single layer structural design requirement. To utilize the superior optical properties of single crystalline materials, we have designed single crystal silicon micromirrors using the micralyne generalized MEMS (MicraGEM) process with a novel latching system that allows the micromirrors to remain locked in a vertical position during operation