Young-Sam Jeon

PZT actuated micromirror for nano-tracking of laser beam for high-density optical data storage

A micromirror actuated by piezoelectric cantilevers is proposed as a fine-tracking device for high-density optical data storage. Metal/PZT/metal thin film actuators translate an integrated micromirror along the out-of-plane vertical direction. The parallel motion of the micromirror steers linearly the optical path of the reflected laser beam. Numerical analysis shows that the actuated micromirror can satisfy the tracking speed imposed by the requirement on the access time for the high-density optical data storage up to few tens Gbit/in/sup 2/. In this paper, preliminary characteristics of the micromachined PZT actuated micromirror (PAM) are reported. The design and the fabrication process of the PZT actuated micromirror are described. Only a 3600 /spl Aring/-thick PZT film deposited by sol-gel process shows both good electrical and mechanical characteristics for the actuators. The micromirror can be easily actuated up to several micrometers under low voltage operation condition.

A micromachined robust humidity sensor for harsh environment applications

This paper reports a high-sensitive robust humidity sensor using a pair of thermally isolated membranes on which includes meander shaped metal resistive elements are formed. The sensing mechanism of the humidity sensor is based on the difference of thermal conductivity with the amount of moisture in air. The sensor exhibits a sensitivity of 0.054 mV/%RH and a response time of 25 sec. Measurements show a remarkably small nonlinearity of 1% FS and a hysteresis of below 2% over a wide range from 40 to 90% RH. Various reliability tests required for practical use in food processing applications, such as a long-term stability test in high/low temperature (150/spl deg/C/-70/spl deg/C) and high humidity (95% RH) environment and a contamination test, reveal its superior durability in harsh environment.

Micromachined silicon optical bench for the low-cost optical module

A novel self-aligning silicon optical bench for fully passive alignment of optical components and its fabrication method are presented. Key technologies developed in this work are multi- step silicon anisotropic etching for manufacturing SiOB, photolithography on three-dimensional surface, precise size control of optical active chip, and flux- and pressure-free die bonding technology. The measured size tolerance of silicon grooves for the active chip and the fiber reveals less than plus or minus 0.5 micrometer. The photolithography process on three-dimensional surface of each site is investigated to get the patterns for deposition of electrodes, mirror, and solders, respectively. The precisely cleaved laser diode chip is obtained by V-groove etching to define the cleaving lane. This technique allows the chip to be defined with a dimensional accuracy of plus or minus 0.5 micrometer. In addition, the pressure-free bonding technique using the electroplated Au-Sn solder makes it possible to reduce the production cost. The fabricated SiOB does not need any pre- alignment process of the optical chip and fiber to desired position such as index alignment method. On the basis of these technologies, it is shown that the fully passive alignment of optical component packaging is successfully preformed. The measured results reveal that the coupling efficiency of the laser diode module was achieved better than 8% and the responsivity of the photo diode module was better than 0.85 A/W.

Integrated multiwavelength laser source module with micromachined mirrors

An integrated silicon sub-mount for laser diodes is reported. The objective of this work is to develop a miniaturized laser source module with switchable wavelengths to use a common optics for different optical data storage media. Patterned thick photoresist: SU-8 is adopted as a micromirror structure in conjunction with proper mirror coating with thin metal film. Photolithographically defined and pre-aligned micromirrors potentially offer an enhanced degree of freedom to optical MEMS designer and greatly reduce the misalignment errors in assembling the optical components. Mesa-shaped mounting seats for assembling the laser diodes, tall vertical sidewall mirrors for reflecting the laser beams emitted from the laser diodes, and deep trench not to disturb the reflected laser beams are integrated on a silicon sub-mount chip by micromachining. The average surface roughness of the metal coated SU-8 sidewall mirrors is well below 1/20 wavelength of the incident laser light of interest, smooth enough for CD or DVD applications. The insertion loss of the vertical sidewall mirror is measured as -0.77 dB when the wavelength of the reflected laser beam is 650 nm.