Arda D. Yalcinkaya

Two-axis electromagnetic microscanner for high resolution displays

A novel microelectromechanical systems (MEMS) actuation technique is developed for retinal scanning display and imaging applications allowing effective drive of a two-axes scanning mirror to wide angles at high frequency. Modeling of the device in mechanical and electrical domains, as well as the experimental characterization is described. Full optical scan angles of 65deg and 53deg are achieved for slow (60 Hz sawtooth) and fast (21.3 kHz sinusoid) scan directions, respectively. In combination with a mirror size of 1.5 mm, a resulting thetasopt D product of 79.5 degmiddotmm for fast axis is obtained. This two-dimensional (2-D) magnetic actuation technique delivers sufficient torque to allow non-resonant operation as low as dc in the slow-scan axis while at the same time allowing one-atmosphere operation even at fast-scan axis frequencies large enough to support SXGA (1280 times 1024) resolution scanned beam displays

Polymer-based stress sensor with integrated readout

We present a polymer-based mechanical sensor with an integrated strain sensor element. Conventionally, silicon has been used as a piezoresistive material due to its high gauge factor and thereby high sensitivity to strain changes in the sensor. By using the fact that the polymer SU-8 [1] is much softer than silicon and that a gold resistor is easily incorporated in SU-8, we have proven that a SU-8-based cantilever sensor is almost as sensitive to stress changes as the silicon piezoresistive cantilever. First, the surface stress sensing principle is discussed, from which it can be shown that the SU-8-based sensor is nearly as sensitive as the silicon based mechanical sensor. We hereafter demonstrate the chip fabrication technology of such a sensor, which includes multiple SU-8 and gold layer deposition. The SU-8-based mechanical sensor is finally characterized with respect to sensitivity, noise and device failure. The characterization shows that there is a good agreement between the expected and the obtained performance.

Electromagnetically Actuated FR4 Scanners

A torsional micromechanical scanner is fabricated from thin fire resistant 4 substrates using standard printed circuit board technology. The top and the bottom copper layers are connected with vias and shaped as a single coil to enable one- and two-dimensional electromagnetic actuation with an external magnet. Using 5 mm times 5 mm mirrors, the following scan angle and resonant frequency combinations are achieved: 17deg at 1.8 kHz and 140deg at 417 Hz. Another 10times improvement in magnetic actuation torque seems feasible. The technology offers a unique advantage by allowing a high degree of integration with microoptics and electronics directly on the mechanical platform and offers a low-cost alternative to silicon microelectromechanical systems devices particularly when large or low-frequency devices are required.

SU-8 based piezoresistive mechanical sensor

We present the first SU-8 based piezoresistive mechanical sensor. Conventionally, silicon has been used as a piezoresistive material due to its high gauge factor and thereby high sensitivity to strain changes in a sensor. By using the fact that SU-8 is much softer than silicon and that a gold resistor is easily incorporated in SU-8, we have proven that a SU-8 based cantilever sensor is almost as sensitive to stress changes as the silicon piezoresistive cantilever. We demonstrate the chip fabrication, and characterization with respect to sensitivity, noise and device failure.

NiFe Plated Biaxial MEMS Scanner for 2-D Imaging

A two-axis microelectromechanical systems micromirror actuator is developed for retinal scanning display and imaging applications. The device operation makes use of magnetostatic torque produced by the combination of a flux generating custom-made high-frequency electrocoil and the NiFe layer deposited on the movable part. Modeling of the actuation in the magnetic domain, as well as the experimental characterization of the mechanical part is described. The device is capable of full optical scan angles of 88deg (at 100-mA root-mean-square coil current) and 1.8deg for slow and fast-scan directions, respectively. In combination with a mirror size of 1.5 mm, resulting thetasoptmiddotD products are 132degmiddotmm and 2.7degmiddotmm for slow and fast axis, respectively. Atmospheric operation of the device is enabled due to high mechanical quality factors of the order of 3000

On heat transfer at microscale with implications for microactuator design

The dominance of conduction and the negligible effect of gravity, and hence free convection, are verified in the case of microscale heat sources surrounded by air at atmospheric pressure. A list of temperature-dependent heat transfer coefficients is provided. In contrast to previous approaches based on free convection, supplied coefficients converge with increasing temperature. Instead of creating a new external function for the definition of boundary conditions via conductive heat transfer, convective thin film coefficients already embedded in commercial finite element software are utilized under a constant heat flux condition. This facilitates direct implementation of coefficients, i.e. the list supplied in this work can directly be plugged into commercial software. Finally, the following four-step methodology is proposed for modeling: (i) determination of the thermal time constant of a specific microactuator, (ii) determination of the boundary layer size corresponding to this time constant, (iii) extraction of the appropriate heat transfer coefficients from a list provided and (iv) application of these coefficients as boundary conditions in thermomechanical finite element simulations. An experimental procedure is established for the determination of the thermal time constant, the first step of the proposed methodology. Based on conduction, the proposed method provides a physically sound solution to heat transfer issues encountered in the modeling of thermal microactuators.

An antenna-coupled split-ring resonator for biosensing

An antenna-coupled split-ring resonator-based microwave sensor is introduced for biosensing applications. The sensor comprises a metallic ring with a slit and integrated monopole antennas on top of a dielectric substrate. The backside of the substrate is attached to a metallic plate. Integrated antennas are used to excite the device and measure its electromagnetic characteristics. The resonant frequency of the device is measured as 2.12 GHz. The characteristics of the device with dielectric loading at different locations across its surface are obtained experimentally. The results indicate that dielectric loading reduces the resonant frequency of the device, which is in good agreement with simulations. The shift in resonant frequency is employed as the sensor output for biomolecular experiments. The device is demonstrated as a resonant biomolecular sensor where the interactions between heparin and fibroblast growth factor 2 are probed. The sensitivity of the device is obtained as 3.7 MHz/(μg/ml) with respe...

Design and fabrication of two-axis micromachined steel scanners

This paper presents the fabrication and the test results of two-axis micromachined micro-mirror steel scanners developed for display and imaging applications. The novel fabrication method uses the conventional lithography and electrochemical metal etching techniques. A single photomask is used to define the whole structure, resulting in a simple and inexpensive fabrication process. Two different devices are designed, fabricated and characterized to test the proposed methods. Both of them employ the magnetostatic actuation to generate excitation force/torque. First device (Type-A) is a gimballed cantilever one, and it is capable of an optical scanning angle of 11.7° and 23.2° in slow- and fast-scan directions, consuming a power of 42 mW and 30.6 mW, respectively. This structure has a quality factor of 287 in the slow-scan direction and a quality factor of 195 in the fast-scan one. The second device (Type-B) is a gimballed torsional one, and it has an optical scanning angle of 76° and 5.9° in slow- and fast-scan directions, consuming 37 mW and 39 mW, respectively. This structure has a quality factor of 132 in the slow-scan and 530 in the fast-scan directions, respectively. The maximum total optical scanning angles obtained for the slow- and fast-scan axes are 105° (gimballed torsional device, Type-B) and 42° (gimballed cantilever device, Type-A).

Modeling and Characterization of Soft Magnetic Film Actuated 2-D Scanners

Magnetic behavior of polymer-based scanners is studied in detail with emphasis on a new magnetic actuator model and dc deflection experiments. A 30-mum-thick permalloy sheet is plated on a polymer cantilever scanner and actuated using an external coil. Mechanical and magnetic modeling of the device and experimental results are presented. Shape anisotropy of the thin, soft magnetic film is explored for push and pull operation in different configurations. A new magnetic actuator model is developed based on the distributed point-by-point calculation of the magnetostatic moments and forces across the film surface. This effort helps one to obtain generic equations for magnetic force and torque without limiting the use of the model to the case where magnetic material is assumed to be fully saturated. Two-dimensional (2-D) scanning utilizing the orthogonal modes of the scanner, using only one actuation coil is presented

Optoelectronic CMOS Power Supply Unit for Electrically Isolated Microscale Applications

This paper presents a CMOS power supply unit for electrically isolated microscale applications, where the provision of electrical power is not appropriate through wiring. A miniature fiberoptic platform consisting of an inclined silicon mirror fabricated using bulk micromachining is coupled to the monolithically integrated photodiode/dc-dc converter system, to yield a stand-alone optical power supply. In this approach, the dc/dc converter steps up the voltage of a single CMOS-integrated photodiode to a higher level. A test chip is fabricated using UMC 0.18-μm triple-well CMOS technology to demonstrate the power supply unit. Two different types of photodiodes, namely, a triple-well photodiode and an n-well photodiode are compared. It is found that on-chip triple-well photodiode results in a projected responsivity of 26 mA/W. The dc/dc converter had a maximum efficiency of 56% and is able to boost an input voltage level of 0.5-to-1.2 V. Silicon mirrors coated with 25-nm-thick aluminum are measured to have a reflectivity of 80% for a laser beam at a wavelength of 650 nm. Capability of the overall packaged optoelectronic system, consisting of the optical fiber, silicon mirror, CMOS photodiode, and the dc/dc converter, is demonstrated by generation of an electrical power of 60 μW.