Geun Ho Kim

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.

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.

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.

A micromachined robust humidity sensor for harsh environment applications

This paper reports a high-sensitive robust humidity sensor using a pair of thermally isolated membranes on which includes meander shaped metal resistive elements are formed. The sensing mechanism of the humidity sensor is based on the difference of thermal conductivity with the amount of moisture in air. The sensor exhibits a sensitivity of 0.054 mV/%RH and a response time of 25 sec. Measurements show a remarkably small nonlinearity of 1% FS and a hysteresis of below 2% over a wide range from 40 to 90% RH. Various reliability tests required for practical use in food processing applications, such as a long-term stability test in high/low temperature (150/spl deg/C/-70/spl deg/C) and high humidity (95% RH) environment and a contamination test, reveal its superior durability in harsh environment.

Closed loop solder-lines on heated substrates

Wafer level MEMS vacuum packaging has been newly designed, fabricated, and characterized by utilizing silicon bulk micromachining and closed loop solder-line bonding. For evaluating the proposed MEMS packaging, a packaging specimen is fabricated which comprises of cap and device substrates. AuSn closed loop solder lines are formed on the cap substrate and feedthroughs are fabricated on the device substrate with deflection diaphragms, respectively. The proposed package can be utilized in wafer level packaging, chip scale packaging, and low cost packaging due to the low process temperature, the compatible fabrication sequences with MEMS devices and a specified pressure endurance. It can be also applied in packaging integrated micro-systems comprised of various components, sensors, and actuators with different processing/working temperature by utilizing the closed loop solder-line on the heated substrate.

Locally Heated Low Temperature Wafer Level MEMS Packaging With Closed-Loop AuSn Solder-Lines

In this paper, locally heated closed-loop AuSn solder-line bonding method was proposed and evaluated for a low-temperature, high strength, and hermetic MEMS packaging. We fabricated two different test specimens including substrate-heated specimen and locally heated specimen in order to verify the performance of locally heated method. In air tightness test, the substrate-heated specimen and locally heated specimen show the maximum leak rate of 13.5±9.8×10−10 mbar-l/s and 18.8±9.9×10−10 mbar-l/s with the same internal volume of 6.89±0.2×10−6 l, respectively. In the critical pressure test, any fracture was not found in the bonded specimens at applied pressure of 10±2bar. From these results, we approximately extracted the bonding strength of the proposed bonding process of 3.53±0.07MPa. By EDS (Energy Dispersive X-ray Spectrometer) analysis at bonded interface, we found that bonded interface (between AuSn solder and Ti/Au layer) of substrate-heated specimen was stronger than that of locally heated specimen.Copyright