"Towards Atmospheric Radical Sensing: Fabrication of Junctionless Transistors" - poster for Micro and Nano Engineering (MNE) conference 2022

Abstract:

Down-scaling of complementary metal-oxide-semiconductor (CMOS) technology faces strong challenges. Therefore, new device and logic concepts, advanced nanomaterials, and advanced fabrication techniques have gained importance in the last few decades. Nanomaterials and nanostructures hold the key for next-generation information processing due to their reduced sizes and new properties. Silicon nanowires, in particular, have been used successfully in new electronic devices, including thermoelectric energy harvesting, sensors, and solar cells.

Silicon nanowires, due to their high surface-to-volume ratio, have demonstrated energy efficient devices. In the case of nanowire based field-effect transistors (FETs), excellent control of conductance across the nanowire is achieved through the electrostatic potential applied at the gate. Moreover, nanowires have been used for fabrication of high sensitivity biochemical sensors, since small volumes allow effective control of the electrostatic potential across a nanowire. Such sensors have been used for various applications, including diagnosing cancer biomarkers and viruses, sensing gases such as ammonia (NH₃), nitrogen dioxide (NO₂), and hydrogen (H₂).

One of the new, nanowire based, device concepts mentioned above is the junctionless nanowire transistor (JNT). A JNT consists of a highly doped nanowire channel without p-n junctions, where the flow of carriers is controlled by the gate potential. JNTs have already shown excellent performance as biosensors [7]. In this work, we report on the fabrication of such transistors for detection of atmospheric free radicals. Intrinsic silicon-on-insulator (SOI) wafers are n-doped by ion implantation. Flash lamp annealing is performed for dopant activation and mitigation of implantation defects. Nanowires are fabricated following a top-down approach using electron beam lithography and reactive ion etching. Then, Nickel/Gold contacts are fabricated. Electrical characterisation of the fabricated devices is performed by back-gating the nanowires. The devices show an on/off current ratio of ca. 10⁶. This will be followed by the functionalization of the fabricated devices for the selective and highly sensitive electrical detection of ꞏOH nad ꞏNO₃ atmospheric radicals, which affect the air quality and climate and have direct impact on our lives.