Byeungleul Lee

Bio: Byeungleul Lee is an academic researcher from Korea University of Technology and Education. The author has contributed to research in topics: Gyroscope & Vibrating structure gyroscope. The author has an hindex of 15, co-authored 76 publications receiving 992 citations. Previous affiliations of Byeungleul Lee include Samsung & Seoul National University.

A Study on Wafer Level Vacuum Packaging for MEMS Devices

Abstract: An ew vacuum packaging process at the wafer level is developed for the surface micromachining devices using glass–silicon anodic bonding technology. The rim for the glass–silicon bonding process which is needed to prevent vacuum leakage is built up simultaneously as the structure is being etched. The mechanical resonator is used as a tool for evaluating the vacuum level of the packaging. The inside pressure of the packaged device wa sm easured indirectly by measuring the quality factor of the mechanical resonator. The measured Q factor was about 5 × 10 4 and the estimated inner pressure was about 1 mTorr. It is also possible to change the inside pressure of the packaged devices from 2 Torr to 1 mTorr by varying the amount of Ti getter material. The yield of the vacuum packaging process is about 80% and vacuum degradation was not observed after 1000 h had passed. The developed vacuum packaging process is also applied to resonant accelerometers which need a high vacuum environment to implement higher performance. (Some figures in this article are in colour only in the electronic version)

A study on wafer level vacuum packaging for MEMS devices

Abstract: A new vacuum packaging process at the wafer level is developed for the surface micromachining devices using glass–silicon anodic bonding technology. The rim for the glass–silicon bonding process which is needed to prevent vacuum leakage is built up simultaneously as the structure is being etched. The mechanical resonator is used as a tool for evaluating the vacuum level of the packaging. The inside pressure of the packaged device was measured indirectly by measuring the quality factor of the mechanical resonator. The measured Q factor was about 5 × 104 and the estimated inner pressure was about 1 mTorr. It is also possible to change the inside pressure of the packaged devices from 2 Torr to 1 mTorr by varying the amount of Ti getter material. The yield of the vacuum packaging process is about 80% and vacuum degradation was not observed after 1000 h had passed. The developed vacuum packaging process is also applied to resonant accelerometers which need a high vacuum environment to implement higher performance.

A study on resonant frequency and Q factor tunings for MEMS vibratory gyroscopes

Abstract: A new approach for improving the performance of MEMS vibratory gyroscopes was developed. The methodology suggests a simple way of improving the performance such as the overshoot, settling time and shock immunity by tuning the resonant frequency and the quality factor. The difference in the resonant frequency in two modes (driving and sensing mode) and the quality factors were found to be key factors in determining the dynamics of the gyroscopes. The difference in the frequency could be easily controlled by the electrical stiffness but it was difficult to control the quality factor because it is determined by vacuum level and the shape of structure. An electrostatic feedback technique allowed the control of the quality factor of the micro-gyroscopes. The experimental results show that the magnitude of the resonant peak in the frequency response of the gyroscope is reduced by 58% when the equivalent quality factor of the sensing system is tuned from 264 to 100 at a 100 Hz frequency difference between the driving and sensing modes. The time domain estimation was an approximate 50% reduction in the overshoot and an approximate threefold shortening of the settling time in that case. The estimation in the time domain was based on the simulation because there is no method to measure the transient response of gyroscopes directly.

A vacuum packaged differential resonant accelerometer using gap sensitive electrostatic stiffness changing effect

Abstract: This paper proposes an INS (Inertial Navigation System) grade, surface micro-machined differential resonant accelerometer (DRXL) by using the epitaxially grown thick polysilicon process. This proposed DRXL device produces a differential digital output upon an applied acceleration, and the principle is a gap-dependent electrical stiffness variation of the electrostatic resonator with torsion beam structures. Using this new operating concept, we designed, fabricated and tested the proposed device. The final device was fabricated by using the wafer level vacuum packaging process. The hermetic sealing cap structure was made of Pyrex 7740 glass with Ti layer as gettering material, and this cap wafer was anodically bonded with the polysilicon wafer at vacuum ambience. The measured Q-factor of the vacuum packaged DRXL was about 1/spl times/10/sup 3/ and the estimated inner pressure was about 200[mTorr]. We also achieved 73[Hz] output frequency change per unit G(9.8 m/s/sup c/) input with 12,716[Hz] nominal resonant frequency.

Rotation-type decoupled MEMS gyroscope

Abstract: A rotation-type decoupled MEMS gyroscope including a drive body movable about the X-axis, a sensing body movable about the Z-axis, a medium body moving together with the drive body about the X-axis and the sensing body about the Z-axis. The drive body is fixed on a substrate by a first torsion spring torsion-deformed about the X-axis, and the medium body is connected to the drive body by a first bending spring bending-deformed about the Z-axis. The sensing body is connected to the medium body by a second torsion spring torsion-deformed about the X-axis and fixed to the substrate by a second bending spring bending-deformed about the Z-axis. If angular velocity is applied relative to the Y-axis while the drive body vibrates in a certain range about the X-axis by a driving electrode, the sensing body rotates about the Z-axis by the Coriolis force and a sensing electrode senses the rotation.

Micromachined inertial sensors

Abstract: This paper presents a review of silicon micromachined accelerometers and gyroscopes. Following a brief introduction to their operating principles and specifications, various device structures, fabrication, technologies, device designs, packaging, and interface electronics issues, along with the present status in the commercialization of micromachined inertial sensors, are discussed. Inertial sensors have seen a steady improvement in their performance, and today, microaccelerometers can resolve accelerations in the micro-g range, while the performance of gyroscopes has improved by a factor of 10/spl times/ every two years during the past eight years. This impressive drive to higher performance, lower cost, greater functionality, higher levels of integration, and higher volume will continue as new fabrication, circuit, and packaging techniques are developed to meet the ever increasing demand for inertial sensors.

Controlling and accessing content using motion processing on mobile devices

Abstract: Various embodiments provide systems and methods capable of facilitating interaction with handheld electronics devices based on sensing rotational rate around at least three axes and linear acceleration along at least three axes. In one aspect, a handheld electronic device includes a subsystem providing display capability, a set of motion sensors sensing rotational rate around at least three axes and linear acceleration along at least three axes, and a subsystem which, based on motion data derived from at least one of the motion sensors, is capable of facilitating interaction with the device.

Interdigital sensors and transducers

Abstract: This review paper focuses on interdigital electrodes-a geometric structure encountered in a wide variety of sensor and transducer designs. Physical and chemical principles behind the operation of these devices vary so much across different fields of science and technology that the common features present in all devices are often overlooked. This paper attempts to bring under one umbrella capacitive, inductive, dielectric, piezoacoustic, chemical, biological, and microelectromechanical interdigital sensors and transducers. The paper also provides historical perspective, discusses fabrication techniques, modeling of sensor parameters, application examples, and directions of future research.

A three-axis micromachined accelerometer with a CMOS position-sense interface and digital offset-trim electronics

Abstract: This paper describes a three-axis accelerometer implemented in a surface-micromachining technology with integrated CMOS. The accelerometer measures changes in a capacitive half-bridge to detect deflections of a proof mass, which result from acceleration input. The half-bridge is connected to a fully differential position-sense interface, the output of which is used for one-bit force feedback. By enclosing the proof mass in a one-bit feedback loop, simultaneous force balancing and analog-to-digital conversion are achieved. On-chip digital offset-trim electronics enable compensation of random offset in the electronic interface. Analytical performance calculations are shown to accurately model device behaviour. The fabricated single-chip accelerometer measures 4/spl times/4 mm/sup 2/, draws 27 mA from a 5-V supply, and has a dynamic range of 84, 81, and 70 dB along the x-, y-, and z-axes, respectively.

MEMS Laser Scanners: A Review

Abstract: Laser scanners have been an integral part of MEMS research for more than three decades. During the last decade, miniaturized projection displays and various medical-imaging applications became the main driver for progress in MEMS laser scanners. Portable and truly miniaturized projectors became possible with the availability of red, green, and blue diode lasers during the past few years. Inherent traits of the laser scanning technology, such as the very large color gamut, scalability to higher resolutions within the same footprint, and capability of producing an always-in-focus image render it a very viable competitor in mobile projection. Here, we review the requirements on MEMS laser scanners for the demanding display applications, performance levels of the best scanners in the published literature, and the advantages and disadvantages of electrostatic, electromagnetic, piezoelectric, and mechanically coupled actuation principles. Resonant high-frequency scanners, low-frequency linear scanners, and 2-D scanners are included in this review.