Myung-Won Lee

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.

Investigation of possible replacement of protective magnesium oxide layer in plasma display panels by barium ternary oxides

The firing voltage (FV) of gas discharge in a test cell of plasma display materials was investigated for standard protective layers of MgO deposited by electron beam, and ternary BaY2O4 and BaGa2O4 oxides grown by pulsed laser deposition on the special dielectric coated glass substrates. The determined FVs for MgO (160 V), BaY2O4 (210 V) and BaGa2O4 (257 V) lead to the conclusion that a replacement of MgO by these ternary oxides is not expedient for plasma display panels. Using results from luminescence spectroscopy, values for the energy gap Eg ≈ 6.2 and 5.8 eV were estimated for BaY2O4 and BaGa2O4, respectively. The main reason for the observed high FVs is attributed to strong electron affinities χ, where χ (BaY2O4) < χ (BaGa2O4).

Switching and memory characteristics of thin films of an ambipolar organic compound: effects of device processing and electrode materials

We report on the effects of device processing conditions, and of changing the electrode materials, on the switching and negative differential resistance (NDR) behaviour of metal/organic thin film/metal structures. The organic material was an ambipolar molecule containing both electron transporting (oxadiazole) and hole transporting (carbazole) chemical groups. Switching and NDR effects are observed for device architectures with both electrodes consisting of aluminium; optimized switching behaviour is achieved for structures incorporating gold nanoparticles. If one of the Al electrodes is replaced by a higher work function metal or coated with an electron-blocking layer, switching and NDR are no longer observed. The results are consistent with a model based on the creation and destruction of Al filaments within the thin organic layer.