Heon Min Lee

NANOSCALE INVESTIGATION OF DOMAIN RETENTION IN PREFERENTIALLY ORIENTED PBZR0.53TI0.47O3 THIN FILMS ON PT AND ON LANIO3

We report results on domain retention in preferentially oriented PbZr0.53Ti0.47O3 (PZT) thin films on Pt and on LaNiO3 (LNO) electrodes. Domain images are obtained by detecting an electrostatic force exerted on the biased conductive probe. We demonstrate that polarization loss of PZT domains on LNO electrodes occurs less under no external field rather than that of PZT on Pt. The time dependence of the remnant polarization is found to follow a stretched exponential decay.

The Emitter Having Microcrystalline Surface in Silicon Heterojunction Interdigitated Back Contact Solar Cells

In producing the Si heterojunction interdigitated backcontact solar cells, we investigated the feasibility of applying amorphous Si emitter having considerable crystalline Si phase at the facing to transparent conducting oxide (TCO) layer. Prior to evaluating electrical property, we characterized material nature of hydrogenated microcrystalline p-type silicon (µc-p-Si:H) as crystallized fraction, surface morphology, bonding kinds in thin films and then surface passivation quality finally. The diode and interface contact characteristics were induced by the simple test device and then current–voltage (I–V) curve showed more linearity in µc/hydrogenated amorphous silicon (a-Si:H) emitter case. We fabricated heterojunction back contact (HBC) solar cells using p/n interdigitated structure and acquired the 23.4% efficiency in cell size with performance parameters as open-circuit voltage (Voc) 723 mV, short-circuit current density (Jsc) 41.8 mA/cm2, fill factor (FF) 0.774, in the cell size (at 2×2 cm2).

Relationship between ion migration and interfacial degradation of CH 3 NH 3 PbI 3 perovskite solar cells under thermal conditions

Organic-inorganic hybrid perovskite solar cells (PSCs) have been extensively studied because of their outstanding performance: a power conversion efficiency exceeding 22% has been achieved. The most commonly used PSCs consist of CH3NH3PbI3 (MAPbI3) with a hole-selective contact, such as 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spiro-bifluorene (spiro-OMeTAD), for collecting holes. From the perspective of long-term operation of solar cells, the cell performance and constituent layers (MAPbI3, spiro-OMeTAD, etc.) may be influenced by external conditions like temperature, light, etc. Herein, we report the effects of temperature on spiro-OMeTAD and the interface between MAPbI3 and spiro-OMeTAD in a solar cell. It was confirmed that, at high temperatures (85 °C), I− and CH3NH3+ (MA+) diffused into the spiro-OMeTAD layer in the form of CH3NH3I (MAI). The diffused I− ions prevented oxidation of spiro-OMeTAD, thereby degrading the electrical properties of spiro-OMeTAD. Since ion diffusion can occur during outdoor operation, the structural design of PSCs must be considered to achieve long-term stability.

Comparison of micromachined FBAR band pass filters with different structural geometry

In this paper, fully integrated FBARs (Film Bulk Acoustic Wave Resonators) and FBAR band pass filters have been designed, fabricated, and characterized for advanced mobile/wireless communication systems by using silicon bulk micromachining technology. Two different band pass filters are fabricated and compared with 7 bulk acoustic resonators in series and shunt connection. Various structures are also investigated for finding the better geometry of the FBAR BPF. In addition, dependency of the quality of AlN film on Mo bottom electrode is also presented. The developed AlN film has 1.9/spl deg/ of FWHM (full width half maximum) of rocking curve and approximately 70 MPa in tensile stress on top of the Mo electrode layer. The measured effective coupling coefficient, K/sup 2//sub effective/ is ranged from 6.8 to 7.3. The fabricated resonator has a quality factor of 1530, insertion loss of -0.45 dB, and return loss of -28 dB, respectively. Fabricated two different (Type-A and Type-B) band pass filters have insertion loss of -1.5 dB and -1.578 dB, return loss of -6 dB and -10 dB, stop band notch of -50 dB and -52 dB, bandwidth of 75 MHz and 70 MHz, 18 MHz and 32 MHz in separation between lower stop band notch and left edge of pass band, and chip size of 1.3 mm /spl times/ 1.5 mm, respectively.

Front contact layer of multiphase silicon-carbon in thin film silicon solar cell

In order to increase the quantum efficiency as well as conversion efficiency, we propose the boron doped hydrogenated multiphase silicon-carbon (called as “multiphase silicon-carbon”) as the front contact layer in thin film silicon solar cells. The multiphase silicon-carbon consists of amorphous carbon, amorphous silicon, and crystalline silicon-like clustering phase. We achieved a high conductivity and a low optical absorptance of multiphase silicon-carbon and compared it with the existing boron doped microcrystalline silicon. Applying this layer between transparent conductive oxide and the p layer, the amorphous silicon and silicon-germanium (a-Si/a-SiGe) double junction cell showed an increase of quantum efficiency in short wavelength and an improvement of the conversion efficiency by about 0.6% in 1 cm2 area.

Thermally driven thin film bulk acoustic resonator voltage controlled oscillators integrated with microheater elements

In this letter, we report on thermally driven thin film bulk acoustic resonator (TFBAR) voltage-controlled oscillators (VCOs) integrated with a microheater element. The oscillation frequency of TFBAR VCOs is controlled by applying different power (or bias voltage) to the microheaters implemented on the TFBAR membrane. The TFBARs with the microheater elements are fabricated by Si bulk micromachining technology. The series feedback schematic TFBAR VCO has an oscillation frequency of 3.566 GHz, an output power of -21 dBm, and a phase noise of -110 dBc/Hz at an offset frequency of 100 kHz. The measured frequency controllability and the measured temperature coefficient of resistance (TCR) of the heater element are 3.19 MHz/V and 0.24%/°C, respectively, with a resistance of 88.1 Ω at room temperature.

A Highly-Sensitive Differential-Mode Microchemical Sensor Using TFBARs with On-Chip Microheater for Volatile Organic Compound (VOC) Detection

In this paper, we first report the microchemical sensor application of differential-mode Thin Film Bulk Acoustic Resonators (TFBARs) for Volatile Organic Compound (VOC) detection. Using the micro heater element, the membrane temperature of TFBARs can be increased up to 250 oC. Generally, VOCs are decomposed to CO and CO2at the temperature of above 200oC, the additional reference oscillator without VOC adsorption can be simply realized by heating the membrane. The RF signal mixer is used to determine the shift in oscillation frequency between sensing and reference oscillators. The frequency responses and sensitivities to benzene, ethanol, and formaldehyde are tested and presented, respectively.

Surface Modification of High Haze Front Transparent Conductive Oxide for Silicon Thin Film Solar Cell

The aluminium-doped zinc oxide (ZnO:Al) films grown by sputtering method were etched to improve the light scattering property. The high haze value (diffuse transmission to total transmission) of above 40% at 850 nm wavelength was obtained by the increase of etching time. But the resistance of film increased and a lot of pin holes were created due to the over etch for high haze. In order to solve these problems, the additional ZnO layer was deposited on etched ZnO:Al film without sacrifice of high haze. This method was able to compensate the deteriorated properties without the change of optical properties. Amorphous based silicon solar cells showed the improvement of photovoltaic performances by the additional deposition.

Surface passivation properties of boron and phosphor-doped a-Si:H films with multi-step deposition for si heterojunction solar cells

Heterojunction, such as the crystalline silicon(c-Si)/hydrogenated amorphous silicon (a-Si:H), forms a high quality passivation properties and developed for a very low recombination contact for photovoltaic devices. As low as doppant concentration (like un-doped or intrinsic), the defect density is decreased and its passivation properties is enhanced, however, in case of emitter or BSF, the low doppant concentration can cause higher contact resistance with TCO or metal electrode simultaneously, so the doping concentration limited by this reason. In this work, we studied the method avoiding doppant concentration limitation in p and n type a-Si:H films with multi layer deposition. The doped p and n type a-Si:H films were divided as two layers, passivation and contacting, through in-situ multistep deposition with different doppant flow rate. The passivation properties of multistep deposited p type a-Si:H films revealed that there were no degradation of lifetime(teff) and implied Voc as increasing doppant concentration, differ from n type case, and showed enhanced open circuit voltage and quantum efficiency at short wavelength.

Microstructures and pyroelectric properties of (Pb,La)TiO3 thin films grown on MgO and ON Pt/MgO

Abstract Comparison has been made between the microstructures and electrical properties of Pb0·95La0·05TiO3 (PLT) thin films deposited on bare (100)MgO and on Pt/(100)MgO. Nearly perfect epitaxial PLT was grown on (100)MgO. (100)-oriented Pt film was obtained via coalescence of Pt islands formed on MgO. Highly c-axis oriented PLT thin film was successfully grown on the Pt bottom electrode with an electrically conductive network structure. High detectivity of 3·5 × 108 and 2·6 × 108 cm√Hz/W was obtained at 30 Hz without any poling treatments from the PLT/MgO- and PLT/Pt/MgO-based infrared detectors, respectively.