Hee Chul Lee

Induction and control of supramolecular chirality by light in self-assembled helical nanostructures

Evolution of supramolecular chirality from self-assembly of achiral compounds and control over its handedness is closely related to the evolution of life and development of supramolecular materials with desired handedness. Here we report a system where the entire process of induction, control and locking of supramolecular chirality can be manipulated by light. Combination of triphenylamine and diacetylene moieties in the molecular structure allows photoinduced self-assembly of the molecule into helical aggregates in a chlorinated solvent by visible light and covalent fixation of the aggregate via photopolymerization by ultraviolet light, respectively. By using visible circularly polarized light, the supramolecular chirality of the resulting aggregates is selectively and reversibly controlled by its rotational direction, and the desired supramolecular chirality can be arrested by irradiation with ultraviolet circularly polarized light. This methodology opens a route to ward the formation of supramolecular chiral conducting nanostructures from the self-assembly of achiral molecules.

Novel concept of TDI readout circuit for LWIR detector

Noise property is the prime consideration in readout circuit design. The output noise caused by the photon noise, which dominates total noise in BLIP detectors, is limited by the integration time that an element looks at a specific point in the scene. Large integration time leads to a low noise performance. Time-delay integration (TDI) is used to effectively increase the integration time and reduce the photon noise. However, it increases the number of dead pixels and requires large integration capacitors and low noise output stage of the readout circuit. In this paper, to solve these problems, we propose a new concept of readout circuit, which performs background suppression, cell-to-cell background current non-uniformity compensation, and dead pixel correction using memory, ADC, DAC, and current copier cell. In simulation results, comparing with the conventional TDI readout circuit, the integration capacitor size can be reduced to 1/5 and trans-impedance gain can be increased by five times. Therefore, the new TDI readout circuit does not require large area and low noise output stage. And the error of skimming current is less than 2%, and the fixed pattern noise induced by cell-to-cell background current variation is reduced to less than 1%.

New Unit Cell of Current Mirroring Direct Injection Circuit for Focal Plane Arrays

In this paper, we propose a new unit cell, named current mirroring direct injection (CMDI) circuit for focal plane arrays. With the current mirroring effect, the circuit designed to control detector bias automatically. Its characteristics are derived analytically, and compared with those of direct injection (DI) and buffered direct injection (BDI). With the CMDI approach, we can achieve almost zero input impedance. Therefore, almost 100% injection efficiency can be obtained even for low RDA values. It has also other advantages such as near zero detector bias, relatively small area and low power consumption.

Stable Ferroelectric Poly(Vinylidene Fluoride-Trifluoroethylene) Film for Flexible Nonvolatile Memory Application

In this letter, a formation method for uniform ferroelectric polymer thin film on very rough aluminum foil is introduced, and the performance characteristics of the film are characterized by hysteresis measurements. For a bending radius of 0.6 cm, the remanent polarization, coercive field and internal bias field are equal in a flat state. After bending 500 times repetitively with a bending radius of 1.1 cm, its performance was nearly constant. Therefore, the method proposed in this letter can be useful for the fabrication of high-quality flexible memory devices on a flexible and rough substrate.

New reflow process for indium bump

A new reflow method for indium bump of hybridized HgCdTe IRFPA is proposed using H2 plasma. Twenty micrometer height indium bump is easily achieved with this method. In the new method, H2 plasma makes the indium bump surface clean with removing the oxidized indium by H radical chemical reaction. Simultaneously, H2 plasma increases the temperature of indium bump above 160 degrees Celsius. This sphere shaped bump is easily deformed plastically with relatively small force. Force of 2 g/bump changes the 20 micrometer height bump to 10 micrometer. The flip-chip bonding technique using the new reflow method is characterized with shear strain strength measurement. It is found that bonding reliability can be improved owing to increased height and smooth surface.

Surface treatment method for 1/f noise suppression in reactively sputtered nickel oxide film

A surface treatment method combined with O2 plasma treatment and Ar+ bombardment is proposed for 1/f noise suppression in a reactively sputtered NiO film as a micro-bolometer sensing material. The 1/f noise power spectral density on a sample prepared by the proposed surface treatment method prior to the contact formation is suppressed to a level roughly 18 times lower than that on an untreated sample. The improved noise characteristic can be ascribed to the cooperative effects of the two steps in the proposed surface treatment method. In its effects, the oxygen plasma treatment is supposed to increase the Ni3+ component on the surface of the NiO film, which in turn increases the hole concentration on the surface. Additional Ar+ bombardment is expected to remove contaminants on the surface of the NiO film, leading to a low contact resistance.

Retention Performance of Ferroelectric Polymer Film for Nonvolatile Memory Devices

For nonvolatile memory devices, capacitors with metal-ferroelectric-metal structures were fabricated using poly(vinylidene fluoride-trifluoroethylene) as a ferroelectric layer, and performance was estimated in terms of retention property. In the same thickness, the polarization retained longer as the writing pulsewidth (PW) was extended. With the same writing PW, a thicker capacitor maintained a polarized state longer. In conclusion, the performance for operating voltage, operating frequency, and data retention time is expected.

Sustainable electronics for nano-spacecraft in deep space missions

An on-the-fly self-healing device is experimentally demonstrated for sustainability of space electronics. A high temperature, which is generated by Joule heating in a gate electrode, provides an on-chip annealing of damages induced by ionizing radiation, hot carrier, and tunneling stress. With the self-healing process, a highly scaled silicon nanowire gate-all-around field-effect transistor shows improved long-term reliability in a logic transistor, floating body DRAM, and charge-trap Flash memory, respectively. A thermally isolated gate structure is proposed to enhance the self-healing effect.

TEC-Less ROIC With Self-Bias Equalization for Microbolometer FPA

This paper describes a new CMOS readout circuit, which makes the microbolometer focal plane array have low spatial noise over a wide operating temperature range without a thermoelectric cooler. The readout circuit corrects the nonuniformity of each microbolometer pixel by the proposed self-bias equalization technique. The proposed readout circuit adopting the self-bias equalization has a feedback loop that makes the readout circuit find the bias voltage for the correction of nonuniformity by itself. The proposed circuit was fabricated using a 0.35-μm standard CMOS process. The measured results of the fabricated chip show that the spatial noise is less than the allowed spatial noise for the equivalent temperature difference of 50 mK over a wide operating temperature range.

A Cantilever-Type Uncooled Infrared Detector With High Fill-Factor and Low-Noise Characteristic

A capacitive microcantilever-type infrared (IR) detector having a unique structure that has high immunity to thermomechanical noise (TM-noise) is proposed. The device has a capacitive readout scheme and is compared with a conventional design using the same readout method by finite element model simulation. The total cantilever length was halved, compared with the conventional device structure, in order to increase the devices spring constant, and the IR absorber area was consequently increased as the portion of the leg in the given pixel area is decreased. Large spring constant and increased absorber area are the main causes of the TM-noise reduction. The feasibility of the device was shown by fabrication, and measured parameters demonstrated the structures superiority. It was shown that the proposed structure potentially has low TM-noise and an overall noise-equivalent temperature difference (NETD) value that is lower than that of the conventional designed device. The NETD of the proposed device was found to be 5.7 mK.