Byeungleul Lee

Simple alignment technique for molding and transfer of 3D PDMS structure using the mechanical alignment jig

Simple alignment technique for the purpose of PDMS molding and transfer is proposed. In order to realize suggested technique, specially designed mechanical jig is devised. This jig helps the mechanical alignment and the clamping of the same-sized wafers. Silicon-on-glass wafer is used as a carrier substrate of the thin PDMS structure. 3D PDMS structure for the cap of sensor has been molded and transferred to the sensor using the jig. Though principle and procedure of alignment is very simple, relatively high alignment precision of 10µm has been achieved. All caps of the sensor chips have survived without peeling during dicing process.

Modal Analysis of a Single-Structure Multiaxis MEMS Gyroscope

This paper reports on designing a single-structure triaxes MEMS capacitive gyroscope which is capable of measuring the three angular velocities on a single drive. A Z-shaped beam for the support of folded coupling spring has been applied to suppress the unwanted mode and decrease the stress effect at the spring ends. The unique coupling spring has changed the driving motion, due to which slide film damping in the driving mode has been reduced. This reduction can lead to higher performance of the sensor with less requirements on vacuum level which decreases the cost of fabrication. Simulation analysis has been performed in COMSOL Multiphysics and Matlab Simulink to finalize the design for fabrication. After finite element analysis, the driving, -sensing, -sensing, and -sensing are, respectively, found to be 13.30 KHz, 13.40 KHz, 13.47 KHz, and 13.51 KHz.

Design and Fabrication of Microelectromechanical Systems Probe Card with Vertical Trench Guide for Fine Pitch Probing

In this study, we developed a new microelectromechanical systems (MEMS) probe card with a vertically guided and electroplated cantilever in order to overcome pitch limitation, which has a compliant structure and is capable of a 35 µm pad pitch, with through-wafer interconnections for IC testing. We also investigated the reliability of the MEMS probe card using tribology and scaling of the MEMS probe card for fine pitch probing. The measured contact resistance was less than 0.5 Ω at 1.5 gf applied force and the leakage current was approximately 10 pA between one tip and an adjacent tip. In addition, the planarity of tips and the alignment of x- and y-axes were satisfied with a conventional needle probe card performance. Therefore, this probe card is suitable for wafer-level burn-in testing and function testing of memory and RF devices.

Wafer level packaged cantilever array type contact force sensor

The wafer level packaged contact force sensor is presented for applications that require fine pitch measurement. The suggested cantilever array type sensor has high spatial resolution of 210µm. To achieve reliable package, the sensor is capped by PDMS soft cap using wafer level molding and bonding process with 10µm alignment precision. The resistance change over contact force was measured to verify the performance. The good linearity of the result confirms that the PDMS package transfers the forces appropriately. The measured sensitivity is about 4.5%/N.

A Study on Measurement Variations in Resonant Characteristics of Electrostatically Actuated MEMS Resonators

Microelectromechanical systems (MEMS) resonators require fast, accurate, and cost-effective testing for mass production. Among the different test methods, frequency domain analysis is one of the easiest and fastest. This paper presents the measurement uncertainties in electrostatically actuated MEMS resonators, using frequency domain analysis. The influence of the applied driving force was studied to evaluate the measurement variations in resonant characteristics, such as the natural frequency and the quality factor of the resonator. To quantify the measurement results, measurement system analysis (MSA) was performed using the analysis of variance (ANOVA) method. The results demonstrate that the resonant frequency (fr) is mostly affected by systematic error. However, the quality (Q) factor strongly depends on the applied driving force. To reduce the measurement variations in Q factor, experiments were carried out to study the influence of DC and/or AC driving voltages on the resonator. The results reveal that measurement uncertainties in the quality factor were high for a small electrostatic force.

Analysis of parasitic feed-through capacitance in MEMS gyroscope with push pull configuration

This work presents the parasitic feed-through capacitance in a MEMS capacitive gyroscope with push-pull configuration. The push-pull configuration was adopted for driving the gyroscope resonator differentially to nullify the linear acceleration effect. The drive mode oscillator of the gyroscope was analyzed theoretically and experiments were carried out to quantize the parasitic feed-through level. It was found that the push-pull configuration worsen the signal to noise ratio by adding up the feed-through noise level at the difference amplifier. We proposed a novel feed-through cancellation scheme after the charge amplifier stage. The experimental results show that, signal to noise ratio (SNR) of 2 dB was achieved without feed-through cancellation. Furthermore, by exploiting the proposed technique, the signal to noise ratio was improved to 28 dB.

Design and analysis of a single-structure three-axis MEMS gyroscope with improved coupling spring

This paper reports the design and analysis of a single drive mass three axis Microelectromechanical systems (MEMS) gyroscope. The proposed MEMS gyroscope contains a unique and simple coupling spring to couple the driving masses. Due to the use of this coupling spring, the stress effect on the spring ends is reduced as it is attached at two points with the driving mass. Moreover, the unwanted motions of the driving mass can be suppressed due to the use of the two spring beams for the support of the central spring. After FEA simulation using COMSOL Multiphysics tool, a first driving mode of the proposed design has been achieved. Other modes were achieved for the pitch, roll and yaw sensing parts. The simulated resonant frequencies are 15.20 kHz for the driving mode, 15.21 kHz for the pitch sensing mode, 15.32 kHz for the roll sensing mode and 15.59 kHz for the yaw sensing mode, respectively.

Fabrication of BeCu module probe array using heating and fusing currents

We have developed a novel probe array using BeCu sheets, to solve the high-production-cost problem associated with conventional MEMS probe cards. The BeCu probe has a simple structure and offers several advantages such as ease of fabrication and rapid prototyping; further, the fabrication process is cost-effective. The proposed array was fabricated by applying a suitable heating current (for plastic deformation via Joule heating) and fusing current (for cutting the array) to a BeCu beam. The stress relaxation time was 7 min during the application of a heating current of 4 A, and the fusing current was 20 A. The fabricated probe array is suitable for use in various complicated semiconductor chip tests.