Mingching Wu

Localized induction heating solder bonding for wafer level MEMS packaging

This paper reports a new solder bonding method for the wafer level packaging of MEMS devices. Electroplated magnetic film was heated using induction heating causing the solder to reflow. The experiment results show that it took less than 1 min to complete the bonding process. In addition, the MEMS devices experienced a temperature of only 110 °C during bonding, thus thin film materials would not be damaged. Moreover, the bond strength between silicon and silicon wafer was higher than 18 MPa. The step height of the feed-through wire (acting as the electrical feed-through of the bonded region) is sealed by the electroplated film. Thus, the flatness and roughness of the electroplated surface are recovered by the solder reflow, and the package for preventing water leakage can be achieved. The integration of the surface micromachined devices with the proposed packaging techniques was demonstrated.

Development of tracking and focusing micro actuators for dual-stage optical pick-up head

This work presents a miniaturized tracking and focusing optical pickup head implemented using MEMS technology. The device was fabricated by poly-Si trench-refilled technology and used a UV-cured polymer droplet or micro ball lens as the objective lens. A bidirectional vertical comb-drive actuator and V-beam thermal actuator drove the objective lens for the out-of-plane (focusing) and in-plane (tracking) motion, respectively. In applications, various tracking and focusing devices have been successfully fabricated and characterized. The upward and downward displacement of the focusing optical pickup head is 2.9 and 1.7 µm, respectively; the in-plane displacement of the tracking optical pickup head is ± 46.7 µm. The resonant frequencies of the focusing and tacking systems are 2.3 and 8.5 kHz respectively. In addition, the UV-cured polymer lens and solid micro ball lens were both successfully integrated with a MEMS device to create an objective lens.

Design and fabrication of MEMS devices using the integration of MUMPs, trench-refilled molding, DRIE and bulk silicon etching processes

This work integrates multi-depth DRIE etching, trench-refilled molding, two poly-Si layers MUMPs and bulk releasing to improve the variety and performance of MEMS devices. In summary, the present fabrication process, named MOSBE II, has three merits. First, this process can monolithically fabricate and integrate poly-Si thin-film structures with different thicknesses and stiffnesses, such as the flexible spring and the stiff mirror plate. Second, multi-depth structures, such as vertical comb electrodes, are available from the DRIE processes. Third, a cavity under the micromachined device is provided by the bulk silicon etching process, so that a large out-of-plane motion is allowed. In application, an optical scanner driven by the self-aligned vertical comb actuator was demonstrated. The poly-Si micromachined components fabricated by MOSBE II can further integrate with the MUMPs devices to establish a more powerful MOEMS platform.

Integrated bi-directional focusing and tracking actuators in a monolithic device for a MEMS optical pick-up head

This work presents a miniaturized two-degree-of-freedom (2-DOF) optical pick-up head implemented using MEMS technology. This device contains novel bi-directional vertical comb-drive actuators to act as the focusing positioner, and V-beam thermal actuators to serve as the tracking positioner. In addition, a UV-cured polymer droplet is used for an objective lens. Particularly, the focusing and tracking actuators are monolithically fabricated and integrated in a single device. Electrical routing and isolation is also available by poly-Si and Si3N4 multi-layers for 2-DOF operation. In applications, the proposed device has been successfully fabricated and characterized. The upward and downward displacements of the focusing optical pick-up head are 4.6 ?m and 4.1 ?m, respectively, at a 30 V driving voltage. And the in-plane displacement of the tracking optical pick-up head is ?16.3 ?m, at a 5 V driving voltage. The resonant frequencies of the focusing and tacking systems are 1.9 kHz and 4.1 kHz, respectively.

Design of Novel Sequential Engagement Vertical Comb Electrodes for Analog Micromirror

The vertical comb-drive actuator (VCA) is a promising component to drive analog as well as scanning micromirrors. This work demonstrates the concept of using ldquosequential engagement of vertical comb electrodesrdquo to improve the linearity and to maximize the deflection for analog micromirror. This concept is achieved by varying the in-plane distribution of comb electrodes. The simulation and experiment results of vertical comb-drive actuator VCA with four different electrode-distribution designs demonstrated the feasibility of this study. In comparison, a modified (curved-profile) VCA was remarkably improved the performance of conventional (straight-profile) VCA. Experiments show that the curved-profile VCA improves the nonlinearity by 34% and increases the maximum angular motion for 2.3-fold.

A Poly-Si-Based Vertical Comb-Drive Two-Axis Gimbaled Scanner for Optical Applications

This work presents a novel two-axis gimbaled mirror for optical scanning applications. This scanner has been implemented using the molded surface-micromachining and bulk etching release (MOSBE II) process. Thus, the vertical comb-drive actuators are employed to realize the large stroke. The thin-film electrical routings are employed to drive the actuators individually. The rib-reinforced structures are exploited to increase the stiffness of mirror plate and supporting frame. In addition, the moving space created by backside deep reactive ion etching enables the mirror to perform large out-of-plane angular motion. The measured radius of curvature of reinforced mirror plate is 0.43 m. The maximum scanning angle of two driving axis are plusmn3.8deg at 55 V and plusmn2.4deg at 100 V, respectively. The resonant frequencies associated with the scanning modes are 5.8 and 7.8m kHz, respectively. In addition, the two-dimensional scanning images such as Lissajous patterns are also demonstrated

A robust and reliable stress-induced self-assembly mechanism for optical devices

Based on the MUMPs platform, this study has established an improved surface micromachining process (MUMPs-like process) to improve the reliability of the stress-induced beams. A novel rigid supporting mechanism is devised to prevent the mirror from offset. Furthermore, with this mechanism various pop-up mirrors could be accomplished. According to this MUMPs-like process, devices are fabricated to evaluate the performance of this assembly mechanism.

Integrated Tracking and Focusing Systems of MEMS Optical Pickup Head

This paper presents a novel bidirectional-driven microelectromechanical systems (MEMS) light manipulation stage. The designed device consists of two actuators integrated with a lens to act as both tracking (in-plane) and focusing (out-of-plane) components for optical pickup head. The actuator is driven by thermal, as well as magnetic, means. According to a static-load deflection test, this device can achieve bidirection actuation with output displacement up to plusmn54.5 mum. In addition, this MEMS device has a very small form factor and provides an excellent response time and size reduction. It can be employed on the portable optical storage system

Integration of the DRIE, MUMPs, and bulk micromachining for superior micro-optical systems

This work integrates multi-depth DRIE etching, two-poly MUMPs, and bulk releasing to accomplish superior poly-Si micro-optical systems. The stiffness of the devices was significantly increased using the trench-refilled rib structure, so that the radius of curvature (ROC) of the 2 /spl mu/m thick mirror even reached 150 mm. In addition, the space between the devices and the substrate was remarkably increased to /spl sim/100 /spl mu/m by bulk silicon etching. Moreover, the self-aligned vertical comb actuators were available through the multi-depth DRIE etching. In application, the scanning mirrors driven by vertical comb actuator were demonstrated. The scanning angle was /spl plusmn/3 degrees (optical angle) at 40 V driving voltages (DC) and resonant frequency was 1.8 kHz. These poly-Si micro-optical devices can further integrate with the MUMPs devices to establish a more powerful MOEMS platform.

A Novel MUMPs-compatible single-layer out-of-plane electrothermal actuator

Microactuator is one of the key components for the microelectromechanical systems (MEMS), and it can be categorized as out-of-plane and in-plane according to the motion types. Most of the existing out-of-plane thermal actuators are multi-layer structures. In this paper, a novel electrothermal single-layer out-of-plane actuator is provided and it characteristics and advantages of this device are stated as follows: (1) This actuator is consisted of only a single thin film material, therefore, it can prevent from delaminating after a long-term operation. Besides, owing to its symmetric geometric design, the inner-beams of this structure don’t have any current passed through them and the inner-beams also provide a geometric constraint to allow the two free ends of the structure to bend upwards symmetrically. (2) This device can be operated at a relative low voltage (<5 volt), and deflected upwards about 4 μm in the experiment test. Besides, the fabrication process is very simple and it is MUMPs(Multi-User MEMS Processes)-compatible. Presently, a prototype structure has been successfully fabricated and tested. This structure offers the potential applications in the adaptive optics systems, and Fabry-Perot filters, etc. Besides, it also provides an interface to cooperate with integrated circuits (IC) and various optical elements to construct an embedded-control optical system.