An image of the nano structures. The organic semiconductor is formed by using CuPC (copper phthalocyanine), PTCDA (3,4,9,10-perylenetetracarboxylic dianhydride). Part of the research was funded by Japan's New Energy and Industrial Technology Development Organization (NEDO). (image courtesy of the University of Tokyo, Kyushu University and NMEMS Technology Research Organization)
The University of Tokyo, Kyushu University and NMEMS Technology Research Organization announced a new technology of improving the sensitivity of silicon (Si)-based near-infrared sensor.
The announcement was made at IEEE MEMS 2014, an international academic conference that took place from Jan 26 to 30, 2014, in San Francisco, the US. The title of the lecture was "Near Infrared Photo-detector Using Self-assembled Formation of Organic Crystalline Nanopillar Arrays." The market for infrared sensors is expanding due to security, elderly care and automotive applications.
The technology was developed by Isao Shimoyama (professor at the University of Tokyo), Chihaya Adachi (professor at Kyushu University), Yoshiharu Ajiki (exchange researcher at NMEMS Technology Research Organization, Olympus Corp), etc. They made a device using Si instead of germanium (Ge). The new method improves detection efficiency by adding 10nm-class metal nano structures to Si to increase electric current generated by receiving lights with certain wavelengths such as infrared light.
This time, the nano structures were realized by using the properties of organic materials, drastically lowering costs compared with conventional methods using lithography, so that the advantage of Si-based device (low cost) is not lost. The nano structures were formed without using expensive lithography equipment by forming organic semiconductor on Si in a self-organized way and forming a gold (Au) film on it.
As a result, it became possible to efficiently extract electric current generated when the nano structures receive 1.2μm-wavelength near-infrared light. Though the nano structures did not seem to be regularly-arranged pillars in the picture of a prototype, the researchers succeeded in improving detection efficiency. Specifically, they improved detection efficiency for wavelengths near 1.2μm by about 20 times with the formation of the nano structures.