Geon-Hee Kim

A new surface-flattening method using single-point diamond turning (SPDT) and its effects on LPE HgCdTe photodiodes

Excellent surface flatness of HgCdTe wafers is essential for fabricating large infrared focal plane arrays (IRFPAs) within the framework of a flip-chip bonding yield. However, liquid-phase epitaxy (LPE) HgCdTe wafers, which are widely used for IRFPAs, have inherent problems pertaining to surface flatness. In this study, we introduced a single-point diamond turning (SPDT) method for use in fabricating LPE HgCdTe photodiodes. The cutoff wavelength of the wafers is ~5 µm. The surface roughness of the LPE HgCdTe wafer has been substantially reduced but a type-converted defective layer was formed on the surface of the HgCdTe wafer after SPDT, which was confirmed using Hall and capacitance–voltage (C–V) measurements. The defective layer, however, was easily removed by bromine in methanol (Br–MeOH) etching. The fabricated photodiode showed a dynamic resistance–area product at the zero bias (R0A) value of ~1 × 104 Ω cm2 for a junction area of 30 × 30 µm2 at 80 K, which is equivalent to that of a conventional photodiode. The flip-chip bonding efficiency has been remarkably improved from 89.43% to 99.99% for 320 × 256 IRFPA at room temperature after SPDT.

Evolutionary grinding model for nanometric control of surface roughness for aspheric optical surfaces

A new evolutionary grinding process model has been developed for nanometric control of material removal from an aspheric surface of Zerodur substrate. The model incorporates novel control features such as i) a growing database; ii) an evolving, multi-variable regression equation; and iii) an adaptive correction factor for target surface roughness (Ra) for the next machine run. This process model demonstrated a unique evolutionary controllability of machining performance resulting in the final grinding accuracy (i.e. averaged difference between target and measured surface roughness) of -0.2+/-2.3(sigma) nm Ra over seven trial machine runs for the target surface roughness ranging from 115 nm to 64 nm Ra.

KASINICS: KASI Near-Infrared Camera System

The Korea Astronomy and Space Science Institute (KASI) is building the KASI Near Infrared Camera System (KASINICS) for the 61-cm telescope at the Sobaeksan Optical Astronomy Observatory (SOAO) in Korea. With KASINICS we will mostly do time monitoring observations, e.g., thermal variations of Jovian planet atmospheres, variable stars, and blazars. We use a 512 x 512 InSb array (Aladdin III Quadrant, Raytheon Co.) for L-band observations as well as J, H, and Ks-bands. The field-of-view of the array is 6 x 6 arcmin with 0.7 arcsec/pixel. Since the SOAO 61-cm telescope was originally designed for visible band observations, we adopt an Offner relay optical system with a Lyot stop to eliminate thermal background emission from the telescope structures. In order to minimize weight and volume, and to overcome thermal contraction problems, we optimize the mechanical design of the camera using the finite-element-method (FEM) analysis. Most of the camera parts including the mirrors are manufactured from the same melt of aluminum alloy to ensure homologous contraction from room temperature to 70 K. We also developed a new control electronics system for the InSb array (see the other paper by Cho et al. in this proceedings). KASINICS is now under the performance test and planned to be in operation at the end of 2006.

DESIGN OF THE OPTICAL SYSTEM FOR A PROTOMODEL OF SPACE INFRARED CRYOGENIC SYSTEM

Many technical challenges are being tried for a large space infrared telescope, which is one of the major objectives of the Strategic Technology Road Map (STRM) of KASI (Korea Astronomy and Space Science Institute), As one of these challenges, KASI and KBSI (Korea Basic Science Institute) have started a cooperation project for developing a space infrared cryogenic system with KIMM (Korea Institute of Machinery as Materials) and i3system co. In this paper, we generate optical requirements for the Protomodel of Space Infrared Cryogenic System (PSICS), and design a single lens optical system with a bandpass of , a field of view of , and an angular resolution of , to develop a further complex optical system.

Design and Performance Analysis of an Off-Axis Three-Mirror Telescope for Remote Sensing of Coastal Water

We report the design and performance analysis of an off-axis three-mirror telescope as the fore optics for a new hyperspectral sensor aboard a small unmanned aerial vehicle (UAV), for low-altitude coastal remote sensing. The sensor needs to have at least 4 cm of spatial resolution at an operating altitude of 500 m, field of view (FOV), and a signal to noise ratio (SNR) of 100 at 660 nm. For these performance requirements, the sensor`s optical design has an entrance pupil diameter of 70 mm and an F-ratio of 5.0. The fore optics is a three-mirror system, including aspheric primary and secondary mirrors. The optical performance is expected to reach in RMS wavefront error and 0.75 in MTF value at 660 nm. Considering the manufacturing and assembling phase, we determined the alignment compensation due to the tertiary mirror from the sensitivity, and derived the tilt-tolerance range to be 0.17 mrad. The off-axis three-mirror telescope, which has better performance than the fore optics of other hyperspectral sensors and is fitted for a small UAV, will contribute to ocean remote-sensing research.

The Effect of Ultrasonic Vibration Table on ELID Grinding Process of Aluminum Nitride Ceramics

This study has focused on the effect of ultrasonic vibration table in ELID grinding process of aluminum nitride ceramics. Aluminum nitride ceramics has superior physical and chemical properties and widely used in IC, LSI substrate, package and so on. To achieve the high effective machining of brittle and high strength ceramics as like aluminum nitride, machining method combined ELID grinding and ultrasonic vibration has been adopted in this study. From the experimental results, material removal rate, MRR has been increased maximum 36 percent and spindle resistance has been decreased in using ultrasonic table. Surface roughness of ground surface became a little worse in using ultrasonic table but was somewhat improved in feed direction.

Properties of ELID Mirror-Surface Grinding for Single Crystal Sapphire Optics

This study has been focused on application of ELID mirror-surface grinding technology for manufacturing single crystal optic sapphire. Single crystal sapphire is a superior material with optic properties of high performance as light transmission, thermal conductivity, hardness and so on. Mirror-surface machining technology is necessary to use sapphire as optic parts. The ELID grinding system has been set up for machining of the sapphire material. According to the ELID experimental results, it shows that the surface of sapphire can be eliminated by metal bonded wheel with micron abrasives and the surface roughness of 60nmRa can be gotten using grinding wheel of 2,000 mesh in 4.5um, depth of cut. In this study, the chemical experiments after ELID grinding also has been conducted to check chemical reaction between workpiece and grinding wheel on ELID grinding process. It shows that the chemical reaction has not happened as the results of the chemical experiments.

Free-Form Surface Reconstruction Method from Second-Derivative Data

We present an algorithm for surface reconstruction from the second-derivative data for free-form aspherics, which uses a subaperture scanning system that measures the local surface profile and determines the three second-derivative values at those local sampling points across the free-form surface. The three second-derivative data were integrated to get a map of x- and y-slopes, which went through a second Southwell integration step to reconstruct the surface profile. A synthetic free-form surface 200 mm in diameter was simulated. The simulation results show that the reconstruction error is 19 nm RMS residual difference. Finally, the sensitivity to noise is diagnosed for second-derivative Gaussian random noise with a signal to noise ratio (SNR) of 16, the simulation results proving that the suggested method is robust to noise.

Development of the Earth Observation Camera of MIRIS

We have designed and manufactured the Earth observation camera (EOC) of multi-purpose infrared imaging system (MIRIS). MIRIS is a main payload of the STSAT-3, which will be launched in late 2012. The main objective of the EOC is to test the operation of Korean IR technology in space, so we have designed the optical and mechanical system of the EOC to fit the IR detector system. We have assembled the flight model (FM) of EOC and performed environment tests successfully. The EOC is now ready to be integrated into the satellite system waiting for operation in space, as planned.

FABRICATION AND ALIGNMENT OF PARTS OF THE KASINICS OFFNER SYSTEM

The KASINICS (KASI Near Infrared Camera System) is a ground-based Near-Infrared (NIR) imaging instrument developed by the Korea Astronomy and Space Science Institute (KASI). In this paper, we report the test results of the KASINICS camera optics system which is comprised of a 1-1 Offner relay. We measure that the surface RMS fluctuations of the Offner mirrors are at the level of of the target wavelengths, showing that the mirrors are sufficiently smooth for NIR observations. The alignment of the Offner optics system has been checked too. Our ray-tracing simulations find that the image quality should not degrade more than the pixel size of the KASINICS (), if a de-centering or a tilt of the Offner mirrors are within 5mm, or . Our measurement shows that the de-centering or the tilt of the Offner mirrors are less than 1 mm or , assuring that the KASINICS image quality are not affected by the alignment errors. We have also measured that the optics resolution is and it does not degrade more than 10% over the detector surface area of 14.3 mm 14.3mm. Overall, we conclude that the KASINICS optics system satisfies the design requirements for NIR imaging observations.