Kwy-Ro Lee

Light extraction enhancement from nano-imprinted photonic crystal GaN-based blue light-emitting diodes.

The nano-imprint lithography method was employed to incorporate wide-area (375 x 330 mum(2)) photonic-crystal (PC) patterns onto the top surface of GaN-based LEDs. When the 280-nm-thick p-GaN was partly etched to ~140 nm, the maximal extraction-efficiency was observed without deteriorating electrical properties. After epoxy encapsulation, the light output of the PC LED was enhanced by 25% in comparison to the standard LED without pattern, at a standard current of 20 mA. By three-dimensional finite-difference time-domain method, we found that the extraction efficiency of the LED tends to be saturated as the etch-depth in the GaN epitaxial-layer becomes larger than the wavelength of the guided modes.

A Wide-Band CMOS Variable-Gain Low Noise Amplifier for Multi-Standard Terrestrial and Cable TV Tuner

A CMOS wide-band low noise amplifier (LNA) based on the current amplification for the multi-standard terrestrial and cable tuner is proposed. Conventional wide-band LNAs suffer from the tradeoff between noise figure and wide-band input matching. By adopting the structure combined the common source (CS) amplifier with the common gate (CG) amplifier by the current amplification, the noise figure does not have any influence on wide-band input matching so that we can achieve low noise figure by the noise canceling and excellent wide-band input matching at the same time while allowing some variable gains. The proposed LNA is fabricated in 0.18-mum CMOS process and achieves a power gain of +15.5~-5.5 dB, an average noise figure of 3.6 dB, an IIP3 of -1 dBm at the maximum gain, and S11 of -15 dB. The power consumption is 50.4 mW and chip area is 0.54 mm2.