Hee-Moon Jeong

Silicon micro XY-stage with a large area shuttle and no-etching holes for SPM-based data storage

A micro XY-stage with a 5/spl times/5 mm/sup 2/-area shuttle is fabricated for application in a nanometer-scale data storage device. A central shuttle of the device is designed as a large square on which a high-density recording medium is deposited. Perpendicularly combined comb-drive actuators allow the large shuttle free access in the x-y plane. No etching holes on the central shuttle are preferred in order to maximize the effective recording area. Therefore, a novel release process, Micro-Channel Assisted Release Process (/spl mu/CARP) is proposed to release a large plate structure without any etching holes and to resist downward sticking. The static and dynamic strokes of the device were measured. Mechanical interferences between x-and y-directional drives were estimated by finite-element method (FEM) analysis and compared with the experimental results.

Slow scanning electromagnetic scanner for laser display

A small sized, low power consuming, shock proven optical scanner with a capacitive comb-type rotational sensor for the application of mobile projection display is designed, fabricated, and characterized. To get a 2-D video image, the present device horizontally scans a vertical line image made through a line-type diffractive spatial optical modulator. To minimize, device size as well as power consumption, the mirror surface is placed on the opposite side of the coil actuator. To prevent thermal deformation of the mirror, the mirror is partially connected to the center point of the coil actuator. To be shock proof, mechanical stoppers are constructed in the device. The scanner is fabricated from two silicon wafers and one glass wafer using bulk micromachining technology. The packaged scanner consists of the scanner chip, a pair of magnets, yoke rim, and base plate. The fabricated package size is 9.2×10×3 mm (0.28 cc) and the mirror size is 3×1.5 mm. The scanner chip receives no damage under the shock test with an impact of 2000 G in 1 ms. In the case of a full optical scan angle of 30 deg at 120-Hz driving frequency, linearity, repeatability, and power consumption are measured at 98%, 0.013 deg, and 60 mW, respectively, which are suitable for mobile display applications.

Construction of probe-based data storage with ultra-high areal density

Our probe-based data storage (PDS) system consists of four parts: signal processing module, multi-probe array, xy-planar actuator, and recording media. The signal-processing module has 2 layers attached to each other. The first layer has 3 D wiring, and it is assembled to the second layer (ASIC module) for the signal processing circuit. The multi-probe array is designed to increase recording and reading speed of the data bits. Each probe has cantilever and tip that are characterized by a tip height of 15 /spl mu/m, a tip radius of 15 nm, a natural frequency of 18.75 kHz and a DC sensitivity of 16.7 nm/V. Poly-silicon probe was fabricated by molding technique to produce high aspect ratio tips. The electrostatic planar actuator serves as a scanner that positions the probe to the right place by moving the media in xy-plane. The moving distance was /spl plusmn/40 /spl mu/m at 10/spl plusmn/10 V, DC gain was 3.04 /spl mu/m/V at 4 V, and the resonance frequency was 143 Hz. The: recording media stores the recorded information in the form of electric polarization in ferroelectric materials. Ferroelectric Pb(Zr,Ti)O/sub 3/ thin film is a candidate material for the media, and it can yield a memory density as high as 400 Gb/in/sup 2/ by recording bits as small as 35 nm in diameter. The bits are fully rewritable and retain the information for a generation at the temperature range below than 50 /spl deg/C.

Variable pivot seesaw actuated RF MEMS switch for reconfigurable system application

A DC contact series MEMS switch for reconfigurable antenna system application is designed, fabricated, and its RF characteristics are measured. Variable pivot seesaw concept is applied because this design minimize the driving voltage and prevent stiction of membrane. The proposed switch structure is fabricated on the Si wafer, a coplanar waveguide(CPW) signal lines and electrodes are fabricated on the glass wafer. Both wafer are bonded by anodic bonding method. The designed chip size is within 2 mmx2 mm and it is actuated by electrostatic force. Low actuation voltage has been achieved by means of small distance between signal line and membrane using the design scheme, switching is executed in the pull-in range. Minimum actuation voltage is about 10-12 V, isolation is around 50 dB and insertion loss is about 0.25 dB at 2 GHz.

Thick membrane operated rf microelectromechanical system switch with low actuation voltage

Most researcher who have studied the radio frequency (rf) microelectromechanical system (MEMS) switch has focused on the electrostatic actuation types switch because of this type’s low power consumption, simple fabrication method, and good rf characteristics compared to magnetic, thermal, and piezoelectric driving method. However, most of electrostatic actuation type switch needs high operation voltage compared to other types. One of the reasons that affect the high operation voltage is the bending of the membrane because of an internal stress gradient. This bending increases the gap between electrode and membrane. To solve this problem, the authors developed the thick membrane operated seesaw type rf MEMS switch. This membrane consisted of a pivot under single crystal thick silicon membrane for a seesaw mode operation and a flexible spring for an up-down actuation mode. After the fabrication of this switch, the authors measured its rf characteristics. The minimum actuation voltage was about 12V, the isol...

Slow Scanning Electromagnetic MEMS Scanner for Laser Display

A small size, low power consuming, shock proven optical scanner with capacitive comb type rotational sensor for the application of mobile projection display was designed, fabricated, and characterized. To get a 2-dimensional video image, the present device horizontally scans a vertical line image made through a line-type diffractive spatial optical modulator. In order to minimize device size as well as power consumption, the mirror surface was placed on the opposite side of the coil actuator. To prevent thermal deformation of the mirror, the mirror was partially connected to the center point of the coil actuator. For shock proof, mechanical stoppers were constructed in the device. The scanner was fabricated from two silicon wafers and one glass wafer using a bulk micromachining technology. The packaged scanner consists of the scanner chip, a pair of magnets, yoke rim, and base plate. The fabricated package size is 9.2mmx10mmx3mm (0.28cc) and the mirror size is 3mmx1.5mm. The scanner chip has no damage under the shock test with impact of 2,000G in 1ms. In case of full optical scan angle of 30° at 120Hz driving frequency, linearity and power consumption are measured 98% and 60mW, respectively, which are suitable for mobile display applications.

Fabrication of Micro XY-Stage with Large-Area Rectangular Shuttle using Anodic Bonding Process

The Micro XY-stage with the large area rectangular shuttle (5 mm×5 mm) is fabricated using an anodically bonded fixture. The large area of a stage is prepared for the integration of a large number of nano-structure array or data-recording media with high density. No etching hole on the central stage is preferred to maximize effective area. The novel release process, μ -CARP (Micro Channel Assisted Release Process) is developed to release a large plate structure without etching hole and to resist a downward sticking. The mechanical characteristics of a fabricated device is measured and discussed.

Reliability Assessment of MEMS Gyroscope Sensor

Reliability of MEMS devices is receiving more attention as they are heading towards commercial production. In particular are the reliability and long-term stability of wafer level vacuum packaged MEMS gyroscope sensors subjected to cyclic mechanical stresses at high frequencies. In this study, we carried out several reliability tests such as environmental storage, fatigue, shock, and vibration, and we investigated the failure mechanisms of the anodically bonded vacuum gyroscope sensors. It was found that successful vacuum packaging could be achieved through reducing outgassing inside the cavity by deposition of titanium as well as by pre-taking process. The current gyroscope structure is found to be safe from fatigue failure for 1000 hours of operation test. The gyroscope sensor survives the drop and vibration tests without any damage, indicating robustness of the sensor. The reliability test results presented in this study demonstrate that MEMS gyroscope sensor is very close to commercialization.

Robust Optimal Design of a Decoupled Vibratory Microgyroscope Considering Fabrication Influence

A robust optimal design considering fabrication influence has been performed for the decoupled vibratory microgyroscope fabricated by the bulk micromachining. For the analysis of the gyroscope, a design tool has been developed, by which user can perform the system level design considering electric signal process and the fabrication influence as well as mechanical characteristics. An initial design of the gyroscope is performed satisfying the performances of scale factor (or sensitivity) and phase delay, which depend on the frequency difference between driving and sensing resonant frequencies. The objective functions are formulated in order to reduce the variances of the frequency difference and the frequency in itself by fabrication error. To certify the results, the standard deviations are calculated through the Monte Caries Simulation (MCS) and compared initial deviation that is measured fabricated gyroscope chip.

Thick-membrane-operated radio frequency switches with wafer-level package using gold compressive bonding

An electrostatically actuated radio frequency (rf) switch is fabricated using a thick silicon membrane, and the device is packaged using a high resistivity silicon cap wafer with a gold (Au) thermocompressive bonding method. To achieve an rf switch that can operate at low voltage, a thick membrane with a pivot under the membrane is used. This design makes it possible to maintain the very small gap between the electrodes and the membrane without bending. A cavity with a pivot-patterned silicon wafer and a coplanar waveguide (CPW) signal-line-formed glass wafer is bonded using an anodic bonding method. After a mechanical polishing process, a deep reactive ion etcher is used to fabricate the membrane structure with a spring and a spring bar. To package the fabricated rf switch, an Au thermocompressive bonding process is used. A 1-µm-thick sputtered Au layer is used as intermediate bonding material. The bonding temperature and pressure are 350 °C and 63 MPa, respectively, and the time duration of the bonding is set to 30 min. The electrodes of the switch and the electrical contact pads on the cap wafers are interconnected via a hole and a sputtered Au metal layer. The total size of the complete packaged rf switch is 2.2 × 1.85 mm, and its rf characteristics have been measured using a Hewlett−Packard (HP) 8510C network analyzer. The measured driving voltage is approximately 16 V, the isolation is approximately −38.4 dB, and the insertion loss is approximately −0.43 dB at 2 GHz.