Jong Uk Bu

A surface-tension driven micropump for low-voltage and low-power operations

In this paper, we first report a micropump actuated by surface tension based on continuous electrowetting (CEW). We have used the surface-tension-induced motion of a mercury drop in a microchannel filled with an electrolyte as actuation energy for the micropump. This allows low voltage operation as well as low-power consumption. The micropump is composed of a stack of three wafers bonded together. The microchannel is formed on a glass wafer using SU-8 and is filled with electrolyte where the mercury drop is inserted. The movement of the mercury pushes or drags the electrolyte, resulting in the deflection of a membrane that is formed on the second silicon wafer. Another silicon wafer, which has passive check valves and holes, is stacked on the membrane wafer, forming inlet and outlet chambers. Finally, these two chambers are connected through a silicone tube forming the complete micropump. The performance of the fabricated micropump has been tested for various operation voltages and frequencies. We have demonstrated actual liquid pumping up to 70 /spl mu/l/min with a driving voltage of 2.3 V and a power consumption of 170 /spl mu/W. The maximum pump pressure is about 800 Pa at the applied voltage of 2.3 V with an operation frequency of 25 Hz.

Micromachined RF MEMS tunable capacitors using piezoelectric actuators

In this paper, RF MEMS tunable capacitors with low operation voltage, high linearity, high quality factor, and large tuning ratio have been fabricated by utilizing micromachined piezoelectric actuators. The fabricated tunable capacitor has a C/sub max//C/sub min/ ratio of 3.1 to 1 at bias voltages of 6 V and a quality factor of 210 at 1 GHz.

Electroplated rf MEMS capacitive switches

RF microswitches are newly designed and fabricated with various structural geometry of transmission line, hinge, and movable plate formed by using electroplating techniques, low temperature processes, and dry releasing techniques. In particular, Strontium Titanate Oxide (SrTiO/sub 3/) with high dielectric constant is investigated for high switching on/off ratio and on capacitance as a dielectric layer of a micromechanical capacitive switch. Achieved lowest actuation voltage of the fabricated switches is 8 volts. The fabricated switch has low insertion loss of 0.08 dB at 10 GHz, isolation of 42 dB at 5 GHz, on/off ratio of 600, and on capacitance of 50 pF, respectively. These switches also have high current carry capability due to the use of electroplated Au or Cux.

Electrostatic MEMS variable optical attenuator with rotating folded micromirror

The design and fabrication of an electrostatic MEMS variable optical attenuator (VOA) is described. The VOA is a reflection type with a folded micromirror actuated by a comb-drive actuator. The VOA is fabricated by a simple single-mask process. One photolithography and subsequent deep silicon reactive ion etching define all the microstructures of the VOA. The folded micromirror structure can reduce the overall size of the device by enabling the parallel alignment of an input fiber and an output fiber. Lensed fibers are used to maximize the coupling efficiency and the ease of assembly. The electrooptic characteristics and dynamic characteristics of fabricated VOA are measured. The initial insertion loss is 0.5 dB at 1550 nm and the maximum attenuation is 45 dB, respectively. The polarization dependent loss is measured to be 0.2 dB at 20-dB attenuation. The response time for maximum attenuation is less than 5 ms.

A micropump driven by continuous electrowetting actuation for low voltage and low power operations

In this paper we first report a micropump actuated by continuous electrowetting (CEW). We have used the surface-tension-induced motion of a mercury drop in the microchannel filled with an electrolyte as actuation energy. We have fabricated the CEW actuator, silicone rubber pumping membranes and copper flap check valves, and have demonstrated actual liquid pumping up to 63 /spl mu/l/min at the applied voltage of 2.3 Vpp. The maximum pump pressure is about 600 Pa at the applied voltage of 2.3 Vpp with operation frequency of 10 Hz.

Integrated micro optical flying head with lens positioning actuator for small form factor data storage

An integrated MEMS optical flying head(OFH) is presented for a small form factor with high-density portable data storage. It is composed of a high numerical-aperture(NA) objective lens, a micro lens actuator for adjusting the position of the lens, an integrated air-bearing-slider(ABS), and an embedded magnetic-field-modulation(MFM) coil for magneto-optical recording. For adjusting the optimal focal length of the lens, a vertical comb-driven actuator and a parallel plate actuator are adopted. In addition, the area-optimized torsion spring is used for vertical actuation. The ABS structure and the double layer MFM coil are fabricated on a transparent substrate bonded to the silicon actuator. The overall size of the integrated MEMS OFH assembled with the high NA(0.85) objective lens is 3 mm? 1.6 mm? 0.5 mm(in length? width? thickness), which makes it suitable for a portable optical storage device.

Fully integrated micromachined capacitive switches for RF applications

RF micromachined capacitive switches are newly designed and fabricated with various structural geometry of transmission line, hinge, and movable plate formed by using electroplating techniques, low temperature processes, and dry releasing techniques. In particular, Strontium Titanate Oxide (SrTiO/sub 3/) with high dielectric constant is investigated for high switching on/off ratio and on capacitance as a dielectric layer of an integrated capacitive switch. Achieved lowest actuation voltage of the fabricated switches is 8 volts. The fabricated switch has low insertion loss of 0.08 dB at 10 GHz, isolation of 42 dB at 5 GHz, on/off ratio of 600, and on capacitance of 50 pF respectively.

Fabrication and characterization of a low-temperature hermetic MEMS package bonded by a closed loop AuSn solder-line

This paper presents a hermetic MEMS package bonded by a closed-loop AuSn solder-line. We design three different test specimens including substrate heated specimen without interconnection-line (SHX), substrate heated specimen with interconnection-line (SHI) and locally heated specimen with interconnection-line (LHI). Pressurized helium leak tests are carried out for hermetic seal evaluation with the critical pressure test for bonding strength measurement. In hermeticity tests, SHX, SHI and LHI show leak rates of 8.4/spl plusmn/6.7/spl times/10/sup -10/ mbar-l/s, 13.5/spl plusmn/9.8/spl times/10/sup -10/ mbar-l/s and 18.8/spl plusmn/9.9/spl times/10/sup -10/ mbar-l/s with the same internal volume of 6.89/spl plusmn/0.2/spl times/10/sup -6/ l, respectively. The specimens of SHX and SHI, bonded by the substrate heater, show leak rates lower than that of LHI. However, the three test specimens satisfy MIL-STD-883E for hermeticity test of microcircuits. In the additional critical pressure test, no fracture is found in the bonded specimens at applied pressure of 1/spl plusmn/0.1MPa. From these results, we approximately extract the bonding strength of the test specimen of 3.53/spl plusmn/0.07 MPa. We experimentally verify that the LHI shows potential for hermetic MEMS packaging with interconnection-line and short-time bonding processes for mass production.

Micromachined FBAR RF filters for advanced handset applications

In this paper, fully integrated FBAR (Film Bulk Acoustic Wave Resonator) RF BPFs (Band Pass Filters) and a duplexer have been designed, fabricated, and characterized for advanced mobile/wireless communication systems by using silicon bulk micromachining technology. Two different RF band pass filters are realized by combining 6 to 7 resonators in series and parallel connection for two chip FBAR duplexer for CDMA PCS applications. AlN, Mo, and silicon nitride are utilized for realizing the proposed FBAR BPFs and duplexer as a piezoelectric material, electrodes, and a supporting membrane, respectively. The fabricated FBAR filters have insertion loss of -1.46 dB and -1.86 dB, return loss of -13 dB and -10 dB, and stop band rejection of -14 dB, and -33 dB, center frequency of 1.88 GHz and 1.96 GHz, and size of 1.3 mm /spl times/ 1.5 mm, respectively. The demonstrated FBAR duplexer for CDMA PCS applications has insertion loss of -1.3 dB (Min.) and absolute attenuation of -42 dB (Min.) at Tx to Antenna port, while it has insertion loss of -2.3 dB (Min.) and absolute attenuation of -52 dB (Min.) at Antenna to Rx port.

Effect of Oxygen to Argon Ratio on Growth of Bi4Ti3O12 Thin Films on Ir and IrO2 Prepared by Radio-Frequency Magnetron Sputtering

Bismuth titanate, Bi4Ti3O12, thin films were grown on Ir/SiO2/Si and IrO2/SiO2/Si substrates by radio-frequency magnetron sputtering. Crystallinity and surface morphology of the heterostructures were characterized over a wide range of oxygen mixing ratio (OMR) during the deposition. X-ray fluorescence spectra reveal that the cation content of the films is dependent upon the OMR, suggesting that control of Bi to Ti ratio is possible by oxygen content of sputtering ambient. Polarization reversal properties of the BTO films show Pr = +15 µC/cm2 and +12 µC/cm2, respectively.