Sahatiya, Parikshit and Badhulika, Sushmee
(2018)
Fabrication of nanoelectronic devices for applications in flexible and wearable electronics.
PhD thesis, Indian Institute of Technology Hyderabad.
Abstract
Conventional electronic devices fabricated on rigid crystalline semiconductors wafers have evolved with the motivation to miniaturize thereby realizing faster, smaller and densely integrated devices. A parallel research that is rapidly evolving for future electronics is to integrate the property of flexibility and stretchablity to develop human friendly devices. There have been number of reports on fabricating sensors and electronic devices on stretchable, bendable and soft materials like polyimide, polyurethane sponge, natural rubber, cellulose paper, tissue paper etc. using various nanomaterials such as 2D materials, metal oxides, carbon nanomaterials and metal nanowires. These nanomaterials possess excellent electronic, thermal, mechanical and optical properties making them suitable for fabrication of broadband photodetectors, temperature, pressure and strain sensors which find applications in the field of optoelectronics, sensors, medical, security and surveillance.
While most reports on photodetectors focus on improving the responsivity in one region of electromagnetic spectrum by fabricating materials hybrids, the main issue still remains unaddressed which is the inability to absorb wide range of electromagnetic spectrum. Most photodetectors comprise of p-n heterojunction, where one of the material is responsible for absorbance, having metal contacts on p and n type allows for effective separation of photogenerated carriers. But for a broadband photodetector, both the materials of the heterojunction should participate in the absorbance. In such a case, metal contacts on p and n type will trap either the photogenerated electrons or hole which leads to the failure of the device. The first part of the thesis focus on the development of flexible broadband photodetectors based on MoS2 hybrid.
Next chapter of the thesis deals with the improvement of responsivity by fabrication of solution processed heterojunction and piezotronic diode on flexible paper substrate for enhanced broadband photodetector and active analog frequency modulator by application of external mechanical strain. The fabricated MoS2 based
heterojunctions was further utilized at circuit level for frequency modulation. The external applied strain not only modulates the transport properties at the junction which not only enhances the broadband photoresponse but also changes the depletion capacitance of junction under reverse bias thereby utilizing it for frequency modulation at circuit level.
The next part of thesis deals with fabrication of new type of electronic, skin-like pressure and strain sensor on flexible, bio-degradable pencil eraser substrate that can detect pressure variations and both tensile and compressive strain and has been fabricated by a solvent-free, low-cost and energy efficient process. Eraser, serves as a substrate for strain sensing as well as acts as a dielectric for capacitive pressure sensing, thereby eliminating the steps of dielectric deposition which is crucial in capacitive based pressure sensors. Detailed mechanism studies in terms of tunneling effect is presented to understand the proposed phenomena. As a proof of concept, an array of 6 x 8 devices were fabricated and pressure mapping of alphabets “I”, “T” and “H” were plotted which were highly consistent with the shape and weight distribution of the object.
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