Sang-chul Sul

Organic-on-silicon complementary metal-oxide-semiconductor colour image sensors

Complementary metal–oxide–semiconductor (CMOS) colour image sensors are representative examples of light-detection devices. To achieve extremely high resolutions, the pixel sizes of the CMOS image sensors must be reduced to less than a micron, which in turn significantly limits the number of photons that can be captured by each pixel using silicon (Si)-based technology (i.e., this reduction in pixel size results in a loss of sensitivity). Here, we demonstrate a novel and efficient method of increasing the sensitivity and resolution of the CMOS image sensors by superposing an organic photodiode (OPD) onto a CMOS circuit with Si photodiodes, which consequently doubles the light-input surface area of each pixel. To realise this concept, we developed organic semiconductor materials with absorption properties selective to green light and successfully fabricated highly efficient green-light-sensitive OPDs without colour filters. We found that such a top light-receiving OPD, which is selective to specific green wavelengths, demonstrates great potential when combined with a newly designed Si-based CMOS circuit containing only blue and red colour filters. To demonstrate the effectiveness of this state-of-the-art hybrid colour image sensor, we acquired a real full-colour image using a camera that contained the organic-on-Si hybrid CMOS colour image sensor.

Highly miniaturized RF bandpass filter based on thin-film bulk acoustic-wave resonator for 5-GHz-band application

Highly miniaturized RF bandpass filter using a thin-film bulk acoustic wave resonator (TFBAR) is designed and fabricated for 5-GHz-band application. The topology of the fabricated filter is based on a ladder-type configuration that has a common trimming inductor connected concurrently with two shunt TFBARs and the trimming inductor is directly connected to the ground. The role of unit the TFBARs physical characteristics such as the size and thickness of the TFBAR determine the performance of the TFBAR filter, including the effect of the electrical impedance-matching characteristics of the TFBAR filter. The shape of the fabricated TFBARs are tetragons with unparallel sides and the sizes of resonator are smaller than 70/spl times/70 /spl mu/m/sup 2/ to ensure the ranges of impedance-matched filter performance. The insertion loss and bandwidth of fabricated TFBAR filters are less than 2.8 dB and 160 MHz at 3 dB. The out-of-band rejection is over 30 dB. The actual size of filter is smaller than 700/spl times/600 /spl mu/m/sup 2/, including signal and ground pad sizes.

Newly Developed High Q FBAR with Mesa-Shaped Membrane

In this paper, the authors present the newly developed high Q film bulk acoustic resonator (FBAR) which has the piezoelectric AlN film sandwiched between two electrode films and mesa-shaped membrane structure by utilizing poly-Si and XeF2 as a sacrificial layer and dry release gas, respectively. By controlling the etching profile of bottom electrode and sacrificial layer, the poor formation of AlN in the edge region of mesa-shaped membrane could be eliminated. In addition, by reducing the parasitic overlap which both of the electrodes and the piezoelectric layer resides directly on the substrate, the authors improve the characteristics of resonator and filter. When we compare with the typical surface micromachined FBAR, such as resonator having its own Bragg reflector or cavity, we could greatly reduce the needs for tight control of chemical mechanical polishing (CMP) of the layer underneath the resonator. The measured Q value and effective electromechanical coupling coefficient of the resonator with the area of 120times120 mum2 were 1450 and 6.43%. The peak insertion loss (IL) and bandwidth of filter were 0.60 dB and 70 MHz, respectively

Fabrication and MFM study of 60 nm track-pitch discrete track media

Discrete track magnetic recording media with a 60 nm track pitch and prewritten servo patterns were fabricated and tested for read/write performance, and a feasibility analysis of the embedded servo was performed. The fabrication process consisted of ultraviolet nanoimprint lithography (UV-NIL) and sequential ion beam etching on a conventional perpendicular magnetic recording medium. Magnetic patterns were written to the fabricated tracks at 700 kilo flux changes per inch (kFCI) using a spin stand and were read using magnetic force microscopy (MFM), with a resulting signal-to-noise ratio (SNR) of 12.15 dB. The servo pattern was also visualized with MFM. These results demonstrated the feasibility of writing to a 30 nm wide discrete data track and the workability of the embedded servo pattern.