Hae-seok Park

Newly Developed High Q FBAR with Mesa-Shaped Membrane

In this paper, the authors present the newly developed high Q film bulk acoustic resonator (FBAR) which has the piezoelectric AlN film sandwiched between two electrode films and mesa-shaped membrane structure by utilizing poly-Si and XeF2 as a sacrificial layer and dry release gas, respectively. By controlling the etching profile of bottom electrode and sacrificial layer, the poor formation of AlN in the edge region of mesa-shaped membrane could be eliminated. In addition, by reducing the parasitic overlap which both of the electrodes and the piezoelectric layer resides directly on the substrate, the authors improve the characteristics of resonator and filter. When we compare with the typical surface micromachined FBAR, such as resonator having its own Bragg reflector or cavity, we could greatly reduce the needs for tight control of chemical mechanical polishing (CMP) of the layer underneath the resonator. The measured Q value and effective electromechanical coupling coefficient of the resonator with the area of 120times120 mum2 were 1450 and 6.43%. The peak insertion loss (IL) and bandwidth of filter were 0.60 dB and 70 MHz, respectively

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.