Hyoungho Ko

Selective silicon-on-insulator (SOI) implant: a new micromachining method without footing and residual stress

This paper presents a new method for electrically isolating released high aspect ratio single crystal silicon (SCS) MEMS structures. In this method, horizontal dielectric layers are implanted at arbitrary depths in any desired region of a wafer using the sacrificial bulk micromachining (SBM) process. A z-axis microgyroscope is fabricated by the proposed method. The measured noise-equivalent angular rate resolution is 0.0074??s?1, the input range is larger than ?50? s?1, and the measured bandwidth is 7.3 Hz. The proposed method achieves electrical isolation with excellent mechanical stability, and is free from the footing phenomenon and residual stress.

Robust SOI process without footing for ultra high-performance microgyroscopes

A microgyroscope with flat bottom surfaces is fabricated by combining the SOI (silicon on insulator) method with the SBM (sacrificial bulk micromachining) process [1/spl sim/3]. Roughened bottom surfaces and loose silicon fragments are common problems in deep silicon RIE (Reactive Ion Etching) using SOI wafers. In this paper, the silicon fragments are removed and the roughened bottom surfaces are smoothed by the SBM process to achieve robust performance. A gyroscope is fabricated by the proposed method. The measured noise equivalent resolution is 0.0044/spl deg//sec, and the measured bandwidth is 12.8 Hz. The linearity of output is within 7.4% for /spl plusmn/50/spl deg//sec range.

A planar, x-axis, single-crystalline silicon gyroscope fabricated using the extended SBM process

A planar, x-axis, single-crystalline silicon gyroscope is fabricated using one (111) SOI wafer using the extended SBM (sacrificial bulk micromachining) process. The gyroscope uses vertically offset combs to resonate the proof mass in the vertical plane, and lateral combs to sense the Coriolis force in the horizontal plane. The extended SBM process is a simple two-mask process, and because all structural parts and combs are defined in one mask level, there is no misalignment in any structural parts or comb fingers. Furthermore, all vertical dimensions of the structure, including the comb height, comb offset and sacrificial gap, can be defined arbitrarily. In addition, the inherent footing phenomenon in the SOI deep etching is completely eliminated and smooth structural shapes are obtained. The fabricated x-axis gyroscope can resolve 0.1 deg/sec angular rate, and the measured bandwidth is 100 Hz. The reported work represents the first x-axis single-crystalline silicon gyroscope fabricated using only one wafer without wafer bonding. In this paper, SOI wafer was used for electrical isolation, but the same device can be fabricated using other available electrical isolation techniques using only one ordinary (111) wafer, albeit fabrication processes are more complicated.

Why Is (111) Silicon a Better Mechanical Material for MEMS: Torsion Case

This paper shows that using the Finite Element Method (FEM), the torsional stiffness of silicon varies by the least amount on silicon (111) with respect to crystallographic directions, when compared to silicon (100) and (110). The used simulator is ANSYS 5.7 with the element type of Solid 64. As a simulation model, we use a simple torsion system, in which a rotational inertia is attached to the center of clamped-clamped beam with a rectangular cross-section. From the results of the modal analysis, the torsional stiffness is derived using the formula between the natural frequency and the torsional stiffness. Simulation results show that the maximum variations of the torsional stiffness on silicon (111), (100) and (110) are 2.3%, 26.5%, and 31.2%, respectively. This implies that on and silicon wafers, substantially different physical dimensions are necessary for devices with the same torsional characteristics, but with different orientations. Therefore, silicon wafers represent a more suitable substrate to design and fabricate torsional micro and nano systems.Copyright

Low-Power Photoplethysmogram Acquisition Integrated Circuit with Robust Light Interference Compensation

To overcome light interference, including a large DC offset and ambient light variation, a robust photoplethysmogram (PPG) readout chip is fabricated using a 0.13-μm complementary metal–oxide–semiconductor (CMOS) process. Against the large DC offset, a saturation detection and current feedback circuit is proposed to compensate for an offset current of up to 30 μA. For robustness against optical path variation, an automatic emitted light compensation method is adopted. To prevent ambient light interference, an alternating sampling and charge redistribution technique is also proposed. In the proposed technique, no additional power is consumed, and only three differential switches and one capacitor are required. The PPG readout channel consumes 26.4 μW and has an input referred current noise of 260 pArms.

A new isolation method for single crystal silicon MEMS and its application to z-axis microgyroscope

This paper presents a new method for electrically isolating the released high-aspect ratio single crystal silicon MEMS structures. In this method, horizontal dielectric layers are implanted at arbitrary depths in any desired region of a wafer, using the Sacrificial Bulk Micromachining (SBM) process. A z-axis microgyroscope is fabricated by the proposed method. The measured noise-equivalent angular rate resolution is 0.0074/spl deg//sec, the input range is larger than /spl plusmn/ 50/spl deg//sec, and the measured bandwidth is 7.3 Hz. The proposed method achieves electrical isolation with excellent mechanical stability, and is free from the footing phenomenon.

Ultralow-Power Bioimpedance IC With Intermediate Frequency Shifting Chopper

A bioelectrical impedance IC with an intermediate frequency shifting chopper (IFSC) technique driven by a merged clock is presented. The proposed technique enables high-frequency impedance measurements with a narrow bandwidth low-power instrumentation amplifier (IA). The conventional series-connected double choppers required for the frequency shifting operation are replaced with a single chopper driven by a XNOR-merged clock. The proposed IC can measure bioelectrical impedance at a maximum excitation frequency of 1.24 MHz in an IA bandwidth of only 30 kHz. A DC trimming technique that uses a dummy impedance and anti-phase current source can adjust the output offset and prevent output saturation. This DC trimming technique also enables shifting of the impedance measurement scope. The proposed IC is fabricated using 0.13-μm CMOS process, and is shown to achieve a dynamic range of 97.1 dB, and 52 μW of power consumption.

Fully integrated low-noise readout circuit with automatic offset cancellation loop for capacitive microsensors.

Capacitive sensing schemes are widely used for various microsensors; however, such microsensors suffer from severe parasitic capacitance problems. This paper presents a fully integrated low-noise readout circuit with automatic offset cancellation loop (AOCL) for capacitive microsensors. The output offsets of the capacitive sensing chain due to the parasitic capacitances and process variations are automatically removed using AOCL. The AOCL generates electrically equivalent offset capacitance and enables charge-domain fine calibration using a 10-bit R-2R digital-to-analog converter, charge-transfer switches, and a charge-storing capacitor. The AOCL cancels the unwanted offset by binary-search algorithm based on 10-bit successive approximation register (SAR) logic. The chip is implemented using 0.18 μm complementary metal-oxide-semiconductor (CMOS) process with an active area of 1.76 mm2. The power consumption is 220 μW with 3.3 V supply. The input parasitic capacitances within the range of −250 fF to 250 fF can be cancelled out automatically, and the required calibration time is lower than 10 ms.

Light-Controlled Biphasic Current Stimulator IC Using CMOS Image Sensors for High-Resolution Retinal Prosthesis and In Vitro Experimental Results With rd1 Mouse

Retinal prosthetic devices stimulate retinal nerve cells with electrical signals proportional to the incident light intensities. For a high-resolution retinal prosthesis, it is necessary to reduce the size of the stimulator pixels as much as possible, because the retinal nerve cells are concentrated in a small area of approximately 5 mm × 5 mm. In this paper, a miniaturized biphasic current stimulator integrated circuit is developed for subretinal stimulation and tested in vitro. The stimulator pixel is miniaturized by using a complementary metal-oxide-semiconductor (CMOS) image sensor composed of three transistors. Compared to a pixel that uses a four-transistor CMOS image sensor, this new design reduces the pixel size by 8.3%. The pixel size is further reduced by simplifying the stimulation-current generating circuit, which provides a 43.9% size reduction when compared to the design reported to be the most advanced version to date for subretinal stimulation. The proposed design is fabricated using a 0.35 μm bipolar-CMOSDMOS process. Each pixel is designed to fit in a 50 μ m × 55 μm area, which theoretically allows implementing more than 5000 pixels in the 5 mm × 5 mm area. Experimental results show that a biphasic current in the range of 0 to 300 μA at 12 V can be generated as a function of incident light intensities. Results from in vitro.

Map building and path generation for Indoor mobile robot by using global and local views

This paper proposes a novel method to generate an accurate and adaptive path for indoor mobile robots by using the global and local camera views. The three dimensional indoor map is necessary for the robots to navigate in the narrow rooms. Since the previous researches usually used the only camera or the sensors inside the robot, it was not easy to get a global map of the room for navigating. In the proposed system, the cameras with a fish-eye lens, attached along a line of the ceiling or at high-level positions on wall, provide the global views which can show the positions of both the moving robot and the fixed stuffs in the room. Also, the camera installed on the robot can provide the real-time local views, notifying the appearance of unexpected objects on its way and identifying the fixed stuffs like furniture in the room. Combing the global and local views can increase the probability of recognizing the objects around the robotic environment, and can provide more detail information of the three dimensional map for navigating.