Dong-sik Shim

Electronic compass using two-axis micro fluxgate sensing element

This paper presents a micro fluxgate sensor fabricated by Si-based Micro Electro Mechanical Systems (MEMS). To measure X- and Y-axis magnetic fields, two fluxgate sensing elements were perpendicularly aligned. The fluxgate sensor was composed of rectangular-ring shaped magnetic core, solenoid excitation and pick-up coils. The 2 /spl mu/m thick Ni/sub 0.8/Fe/sub 0.2/ (permalloy) magnetic core layer was electroplated with photoresist frame using sputtered Ni/sub 0.8/Fe/sub 0.2/ seed layer. The fabricated fluxgate chip size was 4.5/spl times/2.7 mm/sup 2/. Excellent linear response over the range of -100 /spl mu/T to +100 /spl mu/T was obtained with 210 V/T sensitivity at excitation square wave of 2.8 V/sub p-p/ and 1.2 MHz. When two-axis fluxgate sensing element was rotated in terrestrial field, induced second harmonic voltages from X-and Y-axis were sine and cosine wave without distortion, respectively. It is very useful to commercialize the portable navigation system including north-up and map matching, military research, medical research, and space research.

Micro-fluxgate sensor incorporating solenoid coil and BCB dielectric

In this paper, a miniaturized fluxgate sensor with high sensitivity is presented by increasing the permeability of the magnetic material. The fluxgate sensor is composed of a rectangular-ring shaped magnetic core and closely coupled solenoid excitation and pick-up coils. In order to induce magnetic anisotropy, the magnetic core (permalloy) was electroplated under an external magnetic field of 7000 gauss. We designed three types of fluxgate sensors with a change of magnetic core size and solenoid coil turn number. Excellent linear responses of these sensors were obtained with more than 117 V/T sensitivity over the range of -200 /spl mu/T to +200 /spl mu/T. And the size of the smallest micro-fluxgate sensor was about 1.3/spl times/0.7 mm/sup 2/, excluding pad region.

Micro fluxgate sensor using solenoid driving and sensing coils

This paper describes a MEMS-based micro-fluxgate magnetic sensor composed of solenoid driving coil, sensing coil and rectangular-ring shaped magnetic core. Solenoid coils and magnetic core were separated by benzocyclobutene (BCB) having high resistivity and good planarization characteristics. To take advantage of low cost, small size and low power consumption, MEMS technology was used to fabricate micro fluxgate sensor. Copper coil with 20 /spl mu/m width and 3.5/spl mu/m thickness was electroplated on Cr (300/spl Aring/)/Au (1500/spl Aring/) films for driving and sensing coils. We designed the magnetic core into a rectangular-ring shape to reduce the magnetic flux leakage. Permalloy (NiO/sub 0.8/Fe/sub 0.2/) film with the thickness of 2 /spl mu/m was electroplated under 2000 gauss to induce magnetic anisotropy. The magnetic core had the high DC effective permeability of /spl sim/1,100 and coercivity of /spl sim/0.1 Oe. The fabricated fluxgate sensor had the sensitivity of /spl sim/650 V/T and power consumption of 40 mW at the driving frequency of 2 MHz and the driving voltage of 5 Vp-p.

Investigation of stress in aluminum thin film for MEMS applications

Single layer of aluminum film was sputter deposited on to (100) oriented 4 inch silicon wafer to study effect of film thickness, D.C. power and sputtering gas pressure on the film stress. The as-deposited stress appeared to be increasing as film thickness increases and argon pressure decreases. Thermal stress originated from difference in CTE and temperature variation during and after sputtering seems to be a main factor in room temperature sputter deposited aluminum films. From observation of temperature-stress behavior, it was found that the pure aluminum film has an elastic modulus of 56GPA and compressive yield strength of -100MPA. The yield strength was improved to about -175MPA by alloying with 3wt.%Ti. Titanium alloying also proved to be useful in extending linear elastic region before plastic deformation occurs. However, it was hard to determine the stress level with buckling phenomena of ring/beam microstructures because of imperfections such as stress gradient and thermal deformation. In stead, those diagnostic microstructures could be applied to give an information on whether a plastic deformation was introduced or not in a structure of specific dimension.

Fabrication of vertical moving micro-optical switch for display applications

In this paper, we present a new concept and fabrication of micro optical switch of which application is transmissive display devices. The micro optical switch consists of two parallel plate electrodes and is driven by electrostatic force. The first electrode is patterned on the glass substrate and the second electrode is disposed spaced apart from the first electrode. Each electrode has holes and the holes in each electrode do not overlap with one another. Light passes through the holes in the second electrode via the holes in the first electrode. All dimensions and fabrication process of the micro optical switch were designed to be compatible with Liquid Crystal Display (LCD) fabrication process. The size of the fabricated micro optical switch was 254μm × 254 μm. The micro optical switch was fabricated by surface micromachining. Aluminum was used as electrodes and patterned by plasma etching process. Photoresist was used as a sacrificial layer, which defined the gap between the two electrodes. Plasma ahsing was used to remove the sacrificial layer. Finally, anti-stiction layer was coated by Molecular Vapor Deposition (MVD) process. When voltage was applied, the second electrode moved down and contacted the first electrode. When voltage applying stopped, the second electrode returned to its original position. The voltage required to pull in the second electrode was below than 15 V. The sum of transition time, from on to off-state and from off to on-state, was below than 100 ㎲ and operating frequency was more than the 10 kHz.

MEMS-based micro-optical switch for display devices

This paper presents a micro electromechanical system (MEMS) based micro optical switch for display devices. The size of the micro optical switch was 254 μm × 254 μm. The micro optical switch moves vertically by electrostatic force and consists of two parallel plate electrodes which have rectangular aperture array. The lower electrode was directly patterned on a glass substrate and the upper electrode was suspended by cantilever spring which was supported by anchors. The electrodes were made of thin aluminum film and the gap between two electrodes was 3.3 μm. The thickness of the electrodes was 0.3 μm respectively and the lower electrode was covered with 0.3 μm silicon dioxide. The width of the aperture and the metal were 8 μm and 5 μm respectively. The upper aperture array was aligned with the lower aperture array with 6.5 μm offset horizontally and the overlapping width of the two electrodes was 1.5 μm. The micro optical switch is in open state when no voltage is applied and the light passes through the two electrodes by the leakage or the reflection between the two electrodes. The micro optical switch is in close state when voltage is applied and the light is reflected to the backlight unit. The required voltages for pull in and pull out were 16.0 V and 11.4 V respectively. The switching time was 30 μs from the open state to the closed state and 50 μs from the closed state to the open state.

Optical MEMS and nanophotonics in Samsung Electronics

We introduce recent research activities on optical MEMS (micro-electro-mechanical systems) and nanophotonics in Samsung Electronics. Several key optical devices for commercial applications such as lenses, shutters, switches, and absorbers are discussed. The developed optical MEMS devices are based on various tuning mechanisms by electro active polymer, electrostatic, and micro-electro-fluidic actuation. Also, we discuss applicability of nanophotonic components to infrared imaging applications.