Edin Sarajlic

Advanced plasma processing combined with trench isolation technology for fabrication and fast prototyping of high aspect ratio MEMS in standard silicon wafers

A bulk micromachining technology for fabrication of micro electro mechanical systems (MEMS) in a standard silicon wafer is presented. A fabrication process, suitable for full integration with on-chip electronics, employs advanced plasma processing to etch, passivate and release micromechanical structures in a single plasma system, and vertical trench isolation to obtain electrical isolation between the released components. Distinct electrical domains can be defined even on movable parts. The sophisticated electrical isolation between high-aspect-ratio single-crystal silicon (SCS) components allows simplification of the fabrication and improvement of the performance of existing devices and design of entirely new MEMS. The presented technology is an attractive platform for both fabrication and rapid prototyping of MEMS. This is due to a short processing time, a large freedom of design, high process flexibility and low-cost of the starting SCS substrate relative to SOI substrates. Several example microstructures demonstrating the capabilities of this technology have been successfully fabricated.

Subnanometer Translation of Microelectromechanical Systems Measured by Discrete Fourier Analysis of CCD Images

In-plane linear displacements of microelectromechanical systems are measured with subnanometer accuracy by observing the periodic micropatterns with a charge-coupled device camera attached to an optical microscope. The translation of the microstructure is retrieved from the video by phase-shift computation using discrete Fourier transform analysis. This approach is validated through measurements on silicon devices featuring steep-sided periodic microstructures. The results are consistent with the electrical readout of a bulk micromachined capacitive sensor, demonstrating the suitability of this technique for both calibration and sensing. Using a vibration isolation table, a standard deviation of σ = 0.13 nm could be achieved, enabling a measurement resolution of 0.5 nm (4σ) and a subpixel resolution better than 1/100 pixel.

Versatile trench isolation technology for the fabrication of microactuators

A trench isolation technology employs trenches refilled with dielectric material to create, in a single layer, electrical isolation between mechanically joined components. This paper explores further use of this technology for MEMS fabrication, particularly the fabrication of electrostatic microactuators. Adding extra features to a two-mask trench isolation process new design opportunities, like isolation structures and isolation bumps, are created. The isolation structures can be employed as flexible or rigid connections between movable or fixed components or can serve to prevent the short-circuiting by maintaining the end distance between movable electrodes. The isolation bumps reduce stiction during release and operation, prevent short-circuiting due to an out-of-plane displacement and can serve as etch holes at the same time. The trench isolation technology is used to improve fabrication process of an actuator consisting of a large number of elastic electrodes connected in parallel and in series and to develop a novel low volume, large force (> 1 mN) and nanometer resolution electrostatic actuator for low displacement applications.

High performance bidirectional electrostatic inchworm motor fabricated by trench isolation technology

We report on an electrostatic linear micromotor, which employs built-in mechanical leverage to convert normal deflection of a flexible plate into a small in-plane step and two clamps to enable bidirectional inchworm motion. The motor, measuring 412 /spl mu/m /spl times/ 286 /spl mu/m, is fabricated by a combination of trench isolation technology and standard surface micromachining in a relative simple process. The maximum achieved travel range was /spl plusmn/70 /spl mu/m, limited only by flexure design. Depending on the plate actuation voltage, two operation modes, below and above pull-in of the plate, are demonstrated with an adjustable step size from 0.6 to 7 nm and 49 to 62 nm, respectively. The motor was driven in a broad cycling frequency range from 0 to 80 kHz. Output forces of 1.7 mN are measured at 55 V for both the clamps and plate. The motor was operated for 5 days at a stepping frequency of 80 kHz and has completed a cumulative distance of more than 1500 m in about 34/spl middot/10/sup 9/ steps without any performance deterioration.

Fabrication of 3D nanowire frames by conventional micromachining technology

We report on a simple parallel processing method capable of producing addressable three-dimensional (3D) nanometer-sized structures, such as wires, wire frames and dots. The method, which is fully compatible with standard micromachining, employs isotropic removal of conformally deposited material onto a prepared template, to form nanostructures in the concave corners of the template. The process results in well-defined nanometer scale structures with exact position and spatial arrangement fully determined by the template. An etching mask with nanometer size features and a nanowire pyramid on a freestanding cantilever have been successfully fabricated, demonstrating the feasibility and potential of this technology.

Three-Phase Electrostatic Rotary Stepper Micromotor With a Flexural Pivot Bearing

Electrostatic stepper motors, also known as synchronous variable-capacitance motors, operate by utilizing the electrical energy stored in the variable capacitances formed between the poles of their rotor and stator. We present the design, modeling, and experimental characterization of a three-phase rotary stepper micromotor that employs a flexural suspension of the rotor to avoid any frictional contact during operation, providing precise, repeatable, and reliable bidirectional stepping motion without feedback control. A monolithic micromotor with high-aspect-ratio poles and an integrated three-phase electrical network was fabricated in a standard single-crystal silicon wafer by combining vertical trench isolation and bulk micromachining. The experimental characterization of a prototype having a diameter of 1.4 mm has demonstrated a rotational range of 26° (±13°) at 75 V and a maximum speed of 1.67°/ ms. Half-stepping and microstepping operation modes were demonstrated with step sizes of 1/6° and 1/48°, respectively. The exceptional performance of the motor makes it suitable for use in hard-disk drives as a secondary stage actuator to maintain a constant orientation between the read/write head and the recording tracks.

Wafer-scale fabrication of nanoapertures using corner lithography

Several submicron probe technologies require the use of apertures to serve as electrical, optical or fluidic probes; for example, writing precisely using an atomic force microscope or near-field sensing of light reflecting from a biological surface. Controlling the size of such apertures below 100 nm is a challenge in fabrication. One way to accomplish this scale is to use high resolution tools such as deep UV or e-beam. However, these tools are wafer-scale and expensive, or only provide series fabrication. For this reason, in this study a versatile method adapted from conventional micromachining is investigated to fabricate protruding apertures on wafer-scale. This approach is called corner lithography and offers control of the size of the aperture with diameter less than 50 nm using a low-budget lithography tool. For example, by tuning the process parameters, an estimated mean size of 44.5 nm and an estimated standard deviation of 2.3 nm are found. The technique is demonstrated--based on a theoretical foundation including a statistical analysis--with the nanofabrication of apertures at the apexes of micromachined pyramids. Besides apertures, the technique enables the construction of wires, slits and dots into versatile three-dimensional structures.

Electrostatic Rotary Stepper Micromotor for Skew Angle Compensation in Hard Disk Drive

Circular data tracks in present-day hard disk drives (HDD) are accessed by a read/write head mounted on a support arm, which is swung by a voice coil drive. The orientation of the head relative to a data track varies with the radial position of the track, causing an increase in data track misregistration and limiting the performance of HDD. We present a rotary micromotor which can be used as a secondary stage actuator to maintain a constant orientation between the head and the tracks during disk operation. This electrostatic stepper micromotor, bulk micromachined in a standard monocrystalline silicon wafer, uses flexure pivots to avoid any frictional contact of the rotor, providing precise, repeatable and reliable bidirectional stepping motion without feedback control. The experimental characterization of a prototype having a diameter of 1.4 mm has demonstrated a rotational range of 26° (+/- 13°) at 75 V, a resolution of 1/6° in a coarse stepping mode and a maximum speed of 1.67°/ms.

High-Performance Shuffle Motor Fabricated by Vertical Trench Isolation Technology

Shuffle motors are electrostatic stepper micromotors that employ a built-in mechanical leverage to produce large output forces as well as high resolution displacements. These motors can generally move only over predefined paths that served as driving electrodes. Here, we present the design, modeling and experimental characterization of a novel shuffle motor that moves over an unpatterned, electrically grounded surface. By combining the novel design with an innovative micromachining method based on vertical trench isolation, we have greatly simplified the fabrication of the shuffle motors and significantly improved their overall performance characteristics and reliability. Depending on the propulsion voltage, our motor with external dimensions of 290 μm × 410 mm displays two distinct operational modes with adjustable step sizes varying respectively from 0.6 to 7 nm and from 49 to 62 nm. The prototype was driven up to a cycling frequency of 80 kHz, showing nearly linear dependence of its velocity with frequency and a maximum velocity of 3.6 mm/s. For driving voltages of 55 V, the device had a maximum travel range of ±70 μm and exhibited an output force of 1.7 mN, resulting in the highest force and power densities reported so far for an electrostatic micromotor. After five days of operation, it had traveled a cumulative distance of more than 1.5 km in 34 billion steps without noticeable deterioration in performance.

An electrostatic 3-phase linear stepper motor fabricated by vertical trench isolation technology

We present the design, microfabrication and characterization of an electrostatic 3-phase linear stepper micromotor constructed with vertical trench isolation technology. This suitable technology was used to create a monolithic stepper motor with high-aspect-ratio poles and an integrated 3-phase electrical network in the bulk of a standard single-crystal silicon wafer. The shuttle of the stepper motor is suspended by a flexure to avoid any mechanical contact during operation, enhancing the precision, repeatability and reliability of the stepping motion. The prototype is capable of a maximum travel of +/−26 µm (52 µm) at an actuation voltage of 30 V and a step size of 1.4 µm during a half-stepping sequence.