Byoung-Doo Choi

Automatic ballistocardiogram (BCG) beat detection using a template matching approach

This paper suggests a beat detection method for ballistocardiogram (BCG) from an unconstrained cardiac signal monitoring devices. A fiducial peak point of BCG is an I-J-K complex which corresponds with ventricle contraction and Electrocardiogram (ECG) QRS complex. The goal of the method is extraction of J peak without ECG synchronization. The detection method is based on a “template matching” rule evaluated using a correlation function in a local moving-window procedure. The total beat detection algorithm operates in two stages, template definition stage and beat detection stage with defined template in previous stage. In the first stage, the BCG template is constructed by the expert with an empirical analysis of BCG signal and measurement device. In the second stage, the correlation function calculates an accuracy of template with BCG signal using a local moving-window. The data analysis has been performed on the subjects tested at Seoul National University Hospital Sleep Medicine Center and presents 95.16% of sensitivity and 94.76% of positive predictivity value for the J peak detection.

A novel 3D process for single-crystal silicon micro-probe structures

A new fabrication method for a three-dimensional (3D), single-crystal silicon micro-probe structure is developed. A probe card structure requires tips that are at least 50 μm tall on cantilevers thick enough to withstand a few mN of force as well as 50 μm of tip bending. The cantilever structure also must be able to move at least 50 μm of vertical motion, requiring a large sacrificial gap. The developed 3D fabrication method is based on the surface/bulk micromachining technology, which can fabricate released, high aspect ratio, single-crystal silicon microstructures with high yield using (111) silicon.

A novel fabrication process for ultra-sharp, high-aspect ratio nano tips using (111) single crystalline silicon

This paper presents a novel fabrication process for ultra-sharp nano tips on cantilevers with the radius of curvature of less than 10 nm using an (111) single crystalline silicon wafer. The nano tip height 15 /spl mu/m, and the aspect ratio is greater than 3:1. The cone angle of the tip is 19.5/spl deg/. Fabrication process is based on newly obtained etch characteristic data on silicon (111) and the sacrificial bulk micromachining (SBM) technology. The developed fabrication process is simple and robust, and well suited for ultra-sharp, high-aspect ratio nano tips on cantilevers.

The first sub-deg/hr bias stability, silicon-microfabricated gyroscope

The first sub-deg/hr bias stability gyroscope is fabricated in single crystal silicon using the SBM (sacrificial bulk micromachining) process. The quadrature error is a major concern in MEMS gyroscopes for high performance. To minimize the quadrature error, the fabricated gyroscope has a very flat bottom surface, which gives a highly symmetrical proof mass, and springs, which, in turn, provide high performance levels with significantly reduced quadrature error. The fabricated gyroscope has a bandwidth of 58 Hz, and 4-hr bias stability of 0.3 deg/hr.

A 37 ppm/°C Temperature Compensated CMOS ASIC with ±16 V Supply Protection for Capacitive Microaccelerometers

A high reliability CMOS-MEMS hybrid microaccelerometer system is presented. To enhance the temperature response and to minimize die-to-die variations, a low-noise continuous time front-end architecture with temperature compensation and parasitic cancellation is proposed. The temperature coefficients of the output bias and the scale factor are measured to be 37 ppm/degC and 27 ppm/degC, respectively. The bias instability level of the system is measured to be 42 mug. The integrated +16 V power supply protection block gives the enhanced system reliability and reduced form-factor.

High Performance Microaccelerometer with Wafer-level Hermetic Packaged Sensing Element and Continuous-time BiCMOS Interface Circuit

A microaccelerometer with highly reliable, wafer-level packaged MEMS sensing element and fully differential, continuous time, low noise, BiCMOS interface circuit is fabricated. The MEMS sensing element is fabricated on a (111)-oriented SOI wafer by using the SBM (Sacrificial/Bulk Micromachining) process. To protect the silicon structure of the sensing element and enhance the reliability, a wafer level hermetic packaging process is performed by using a silicon-glass anodic bonding process. The interface circuit is fabricated using 0.8 µm BiCMOS process. The capacitance change of the MEMS sensing element is amplified by the continuous-time, fully-differential transconductance input amplifier. A chopper-stabilization architecture is adopted to reduce low-frequency noise including 1/f noise. The fabricated microaccelerometer has the total noise equivalent acceleration of 0.89 µg/√Hz, the bias instability of 490 µg, the input range of ±10 g, and the output nonlinearity of ±0.5 %FSO.

Two-chip implemented, wafer-level hermetic packaged accelerometer for tactical and inertial applications

A two chip implemented, wafer-level hermetically packaged accelerometer is presented. The accelerometer core is fabricated using the SBM (sacrificial bulk micromachining) process. The fabricated accelerometer core accomplishes high performance, high yield and high reliability by the inherent high-aspect-ratio, footing-free advantages of the SBM process. In order to protect the accelerometer core from environmental changes, a wafer-level hermetic packaging process is performed by using glass-silicon anodic bonding. The capacitive detection circuit adopts an EEPROM trimmable architecture to reduce the die-to-die variations. The fabricated accelerometer has the noise equivalent acceleration resolution of 43 /spl mu/g, input range of /spl plusmn/10 g, Output nonlinearity of 0.1% FSO, scale factor of 130 mV/g, and 4-hr bias stability of 1.10 mg.

DRY AND WET ETCHING WITH (111) SILICON FOR HIGH-PERFORMANCE MICRO AND NANO SYSTEMS

Etching with (111) silicon is relatively new, but it represents very exciting opportunities in micro and nano system applications. By combining wet and dry anisotropic etching, high-precision, actuatable micro and nano structures can be fabricated in single-crystalline silicon. This paper reviews several relevant (111) microfabrication results reported in the literature. Among these, a single-mask process that we call sacrificial bulk micromachining (SBM) is reviewed in detail. Various electrical isolation methods as well as a number of applications to micro and nano systems are presented.

Wafer-level Vacuum Packaged X and Y axis Gyroscope Using the Extended SBM Process for Ubiquitous Robot applications

Abstract A wafer-level vacuum packaged x and y axis gyroscope is fabricated on a (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. The silicon-to-glass anodic bonding carried out in low vacuum is used for the encapsulation of the fabricated gyroscope. The fabricated x and y axis gyroscope resolves 0.7 deg/sec angular rate, and the measured bandwidth is 22 Hz. The input range and the output linearity are over ± 80 deg/sec and 1.03 %FSO, respectively. The fabricated vacuum packaged x and y axis gyroscope without align error is important component at the high performance multiple-axis gyroscopes. The multiple-axis gyroscopes are used in many applications such as recently interested ubiquitous robot, car navigation, game controller, vehicle safety system, and so on.

Estimation of angular velocity and acceleration by using 2 linear acceleration sensors

Abstract This paper presents a method to measure angular velocity with two silicon-based MEMS acceleration sensors which have the resolution of 0.08 mg. This paper proposes measurement results using the technique to compensate the alignment error and estimate an angular velocity with two acceleration sensors fabricated by sacrificial bulk micromachining (SBM) process. The technique also estimates an angular velocity of a commercial cleaning robot, which has been tried to make the unit cost of production lower, by using two acceleration sensors without using a gyroscope.