Ernest J. Garcia

Surface micromachined microengine

Abstract The design, fabrication, and preliminary testing of a polysilicon microengine are presented. In this early work, electrostatic comb-drive actuation is used to demonstrate the microengine. However, the basic gear/link element of the microengine can be driven by any suitably forceful linear actuators. This device has direct application as a drive and power source for micromachined mechanisms such as optical switches, electrical switches, micropositioners, or any other micro-sized device requiring mechanical power. This is the first device of its kind that is directly linked to an output gear and converts linear motion from comb-drive actuators to rotational motion. The microengine provides output in the form of a continuously rotating output gear (≈ 50 μm in diameter) that is capable of delivering torque to a micromechanism. The microengine can be operated at varying speeds and its motion can be reversed. Processing considerations address the elimination of natural interferences that arise when conformally deposited polysilicon films form the links, joints, and gears that comprise the microengine. The resultant device is completely batch fabricated without the need for piece-part assembly.

Microfabricated actuators and their application to optics

Several authors have given overviews of microelectromechanical systems, including microactuators. In our presentation we review some of these results, and provide a brief description of the basic principles of operation, fabrication, and application, of a few selected microactuators (electrostatic and surface tension driven). We present a description of a three- level mechanical polysilicon surface-micromachining technology with a discussion of the advantages of this level of process complexity. This technology is capable of forming complex, batch-fabricated, interconnected, and interactive, microactuated micromechanisms which include optical elements. The inclusion of a third deposited layer of mechanical polysilicon greatly extends the degree of complexity available for micromechanism design. Two examples of microactuators fabricated using this process are provided to illustrate the capabilities and usefulness of the technology. The first actuator is an example of a novel actuation mechanism based on the effect of surface tension at these micro-scale dimensions and of a microstructure within a microstructure. The second is a comb-drive-based microengine which has direct application as a drive and power source for micro optical elements, specifically, micro mirrors and micro shutters. This design converts linear oscillatory motion from electrostatic comb drive actuators into rotational motion via a direct linkage connection. The microengine provides output in the form of a continuously rotating output gear that is capable of delivering drive torque to a micromechanism.

Surface Micromachined Microengane As The Driver For Micromechanical Gears

The transmission of mechanical power is often accomplished through the use of gearing. The recently developed surface micromachined microengine [1] provides us with an actuator which is suitable for driving surface micromachined geared systems. In this paper we will present aspects of the rnicroengine as they relate to the driving of geared mechanisms, issues relating to the design of micro gear mechanisms, and details of a design of a microengine-driven geared shutter mechanism.

Surface micromachined counter-meshing gears discrimination device

This paper discusses the design, fabrication and testing of a surface micromachined Counter-Meshing Gears discrimination device which functions as a mechanically coded lock. A 24 bit code is input to unlock the device. Once unlocked, the device provides a path for an energy or information signal to pass through the device. The device is designed to immediately lock up if any portion of the 24 bit code is incorrect. The motivation for the development of this device is based on occurrences referred to as High Consequence Events. A High Consequence Even is an event where an inadvertent operation of a system could result in the catastrophic loss of life, property, or damage to the environment.

Pivoting micromirror designs for large orientation angles

This paper describes mechanical designed concepts for a class of pivoting micromirrors that permit relatively large angles of orientation to be obtained when configured in large arrays. Micromirror arrays can be utilized in a variety of applications ranging from optical switching to beam-front correction in a variety of technologies. This particular work is concerned with silicon surface micromachining. The multi-layer polysilicon surface micromachined process developed at Sandia National Laboratories is used to fabricate micromirror arrays that consists of capacitive electrode pairs which are used to electrostatically actuator mirrors to their desired positions and suitable elastic suspensions which support the 2 micrometers thick mirror structures. The designs described have been fabricated and successfully operated.

Optical measurement of LIGA milliengine performance

Understanding the parameters that affect the performance of milliscale and microscale actuators is essential to the development of optimized designs and fabrication processes, as well as the qualification of devices for commercial applications. This paper discusses the development of optical techniques for motion measurements of LIGA fabricated milliengines. LIGA processing permits the fabrication of precision millimeter-sized machine elements that cannot be fabricated by conventional miniature machining techniques because of their small feature sizes. In addition, tolerances of 1 part in 103 to 104 may be maintained in millimeter sized components with this processing technique. Optical techniques offer a convenient means for measuring long term statistical performance data and transient responses needed to optimize designs and manufacturing techniques. Optical techniques can also be used to provide feedback signals needed for control and sensing of the state of the machine. Optical probe concepts and experimental data obtained using a milliengine developed at Sandia National Laboratories are presented.

Design and fabrication of a LIGA Milliengine

This paper reports on the design and fabrication of a new milliscale magnetic actuator that is ideally suited for LIGA processing. LIGA processing permits the fabrication of millisized machine elements that cannot be fabricated by conventional miniature machining techniques because of their small feature sizes. The Milliengine is a magnetically driven device that utilizes a unique design to extend the 2-dimensional fabrication capability of LIGA to create 3-dimensional machinery.

SOI-enabled MEMS processes lead to novel mechanical, optical, and atomic physics devices

Beginning in the mid-1990s, Sandia National Laboratories began its migration to Silicon-on-Insulator (SOI) wafers to develop a radiation-hardened semiconductor process for sub-0.5mum geometries. Successfully radiation hardening SOI technologies enabled an in-house processing familiarity that exceeded our expectations by opening opportunities to improve other technologies. Rather than rely on a single SOI technology, we have developed families of SOI processes using SOI wafers specifically tailored for each of a number of diverse applications. From this SOI expertise, we have designed, developed, and fabricated a number of novel devices that exploit a variety of mechanical, electrical, and optical phenomena, including atomic-physics based devices. We present a high-level description of our SOI process technologies using product examples. Of particular note are a novel accelerometer, RF MEMS microresonators and contacting switches, integrated optics (low-loss Si waveguides, the smallest and lowest power micro-ring modulators and thermo-optic phase modulators/switches), and ion traps for quantum computing (along with other atomic physics device examples).

Optical performance of pivoting micromirrors

In this paper we describe optical and dynamic performance of tip/tilt micromachined mirrors fabricated using the SUMMIT V surface micromachining process. We find that the tilt angle for a given mirror design is determined by a combination of geometric factors and stiffness of the capacitive suspension. Switching speeds of ~40-50 microsecond(s) econds are measured for 50 micrometers -square mirrors. Finally surface roughness and curvature before and after metallization are obtained using white light interferometry.

MEMS Closed-Loop Control Incorporating a Memristor as Feedback Sensing Element

In this brief, the integration of a memristor with a microelectromechanical systems (MEMS) parallel plate capacitor coupled by an amplification stage is simulated. It is shown that the MEMS upper plate position can be controlled up to 95% of the total gap. Due to its common operation principle, the change in the MEMS plate position can be interpreted by the change in the memristor resistance or memristance. A memristance modulation of ~1 kΩ was observed. A polynomial expression representing the MEMS upper plate displacement as a function of the memristance is presented. Thereafter, a simple design for a voltage closed-loop control is presented, showing that the MEMS upper plate can be stabilized up to 95% of the total gap by using the memristor as a feedback sensing element. The memristor can play important dual roles in overcoming the limited operation range of MEMS parallel plate capacitors and in simplifying read-out circuits of those devices by representing the motion of the upper plate in the form of resistance change instead of capacitance change.