Yonghwa Park

A novel microneedle array integrated with a PDMS biochip for microfluid systems

This paper reports a novel single-crystal-silicon microneedle array, its mechanical properties, its integration with a polydimethylsiloxane (PDMS) biochip, as well as in vitro and in vivo test results. The fabricated microneedle arrays have integrated microchannels, which are fabricated by using the processes of anisotropic dry etching, isotropic dry etching, and trench-refilling. The microchannel diameter is about 20 /spl mu/m. The 2 mm-length microneedle shaft is strong enough to endure 12.6 gf (=23.5 mN) of vertical loading. The fabricated microneedles are planar, which make it easy to integrate with biofluidic devices. As an in vitro test, the microneedle array is integrated with a PDMS biochip, and black ink is injected into a methanol-filled petri dish. The microneedle is tested in vivo by penetrating the mouse skin and precisely pricking into the small vein in the mouse tail.

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.

Modeling and Simulation of the Microgyroscope Driving Loop using SPICE

A simulation model of vibratory capacitive microgyroscope and its driving loop is designed using SPICE. The vibratory microgyroscope is basically microelectromechanical system; therefore the simulation model should be expressed mechanical and electrical properties. To modelling the microgyroscope, the Analog Behavioral Model is used. In order to design a driving loop of vibratory microgyrosope, the the Barkhausen criteria is considered. The co-simulation of MEMS sensing element and its interface circuit is performed. The SPICE simulation model of the vibratory microgyrocope is designed, and the driving loop of the microgyroscope is simulated using the designed simulation model. The simulation results demonstrate the validity of the designed model and its interface circuit

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 Hermetic Packaged Dual-axis Digital Microaccelerometer

A wafer-level hermetic packaged X/Y dual-axis digital microaccelerometer is presented. The MEMS sensing element of the microaccelerometer is fabricated by the sacrificial bulk micromachining (SBM) process. The two microaccelerometers are fabricated on a same silicon substrate, and thus have a perfect orthogonality. To protect the silicon structure of the sensing element, a wafer-level hermetic packaging process is performed. The interface circuit of the microaccelerometer is fabricated using the 0.18 mum CMOS process. The capacitance change of the sensing element is converted to voltage signal by a charge amplifier. The analog signal is converted to digital signal by an A/D converter and a digital filter. The microaccelerometer has the scale factor of 9839 count/g, the output nonlinearity of 0.35 %FSO, the input range of plusmn0.83 g and the bias instability of 2.2965 mg for the x-axis, and the scale factor of 10087 count/g, the output nonlinearity of 0.38 %FSO, the input range of plusmn0.81 g and the bias stability of 7.1881 mg for the y-axis

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.

MEMS-FABRICATED GYROSCOPES WITH FEEDBACK COMPENSATION

Abstract This paper presents a lead-lag compensator design for a MEMS-fabricated microgyroscope. The microgyroscope is basically a high Q system, thus the bandwidth is limited to be narrow. To overcome the open-loop performance limitations, a feedback controller is designed to improve the resolution, bandwidth, linearity, and bias stability of the microgyroscope. The feedback controller is applied to the z-axis microgyroscope fabricated by SBM process. In MATLAB simulations, resolution, bandwidth, input range, and bias stability of closed-loop system are improved from 0.0021 deg/sec to 0.0013 deg/sec, from 14.8 Hz to 115 Hz, from ±50 deg/sec to ±200 deg/sec, and from 0.0249 deg/sec to 0.0028 deg/sec, respectively.

MEMS-FABRICATED ACCELEROMETERS WITH FEEDBACK COMPENSATION

Abstract This paper presents a feedback-controlled, MEMS-fabricated microaccelerometer. The microaccelerometer has received much commercial attraction, but its performance is generally limited. To improve the open-loop performance, a feedback controller is designed and experimentally evaluated. The feedback controller is applied to the x/y-axis microaccelerometer fabricated by sacrificial bulk micromachining (SBM) process. Even though the resolution of the closed-loop system is slightly worse than open-loop system, the bandwidth, linearity, and bias stability are significantly improved. The noise equivalent resolution of open-loop system is 0.615 mg and that of closed-loop system is 0.864 mg. The bandwidths of open-loop and closed-loop system are over 100 Hz. The input range, non-linearity and bias stability are improved from ±10 g to ±18 g, from 11.1 %FSO to 0.86 %FSO, and from 0.221 mg to 0.128 mg by feedback control, respectively.