News from Nanotechjapan

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Transparent Transistor that Transmits Deep Ultraviolet ---Novel Biosensor---

 On June 16, 2020, Hokkaido University announced that the research group of Professor Hiromichi Ohta from Research Institute for Electronic Science of the university succeeded in demonstrating thin film transistors (TFT) with deep-ultraviolet transparency as a promising component for next generation optoelectronics such as biosensors. Related paper was published in Advanced Electronic Materials*. 

 In the human fight against infection or disease, biosensors are demanded to detect virus and bacteria. Attached DNA of these biomaterials on the active layer of semiconductor devices modifies the electric current through the device, and a Si-based transistor is able to be used as a biosensor. However, detec-tion is frequently performed under ultraviolet (UV) germicidal lamps to result in current fluctuations against stable detection. The reason is the carrier excitation in Si with energy bandgap of 1.1eV, low enough absorbing UV light. The research group challenged to fabricate deep-UV transparent transistors for stable detection.

 Among several deep-UV (DUV) transparent oxide semiconductors, SrSnO3 is selected  for the active layer because of its wide band gap (≈4.6eV) and rather high electrical conductivity (3,000S/cm). Thin film(28 nm)SrSnO3  and gate insulator film (C12A7;300nm) are stacked on SrTiO3 substrate, and TFT was fabricated with channel length/width=800μm/400μm. The resultant TFT shows clear transis-tor characteristics with ON/OFF  current ratio of ≈102, threshold voltage of ≈18 V, and the field effect mobility of ≈14cm2/Vs. Optical property was evaluated by TFT without electrode to show transmission efficiency above 50% for DUV of 260nm wavelength and 90% for wavelength above 300nm.

*Mian Wei, Lizhikun Gong, Dou‐dou Liang, Hai Jun Cho, and Hiromichi Ohta, "Fabrication and Op-erating Mechanism of Deep-UV Transparent Semiconducting SrSnO3- based Thin Film Transistor", Advanced Electronic Materials, Early View, DOI: 10.1002/aelm.202000100; first published: 15 June 2020