Research
Research Projects and key roles:
Project 01: Phase change material based thin-film light sensors
Due to its cheapness, stability, high speed, and ease of integration, silicon is commonly used for light sensors and photodetectors. However, silicon's indirect bandgap limits its optical absorption capabilities. Although the absorption range of other III-V compound semiconductors can extend beyond the near-infrared and into the infrared, their fabrication is complex and expensive. This leads to research on alternative materials that are suitable for broadband light sensing.
The unique band structure of inorganic compound vanadium dioxide and its reversible phase transition from an insulator to a metal above 68°C make it interesting for optoelectronic applications. This phase transition can be triggered by light, heat, and electricity. In addition, being a small bang-gap material of ~0.6 eV, vanadium dioxide absorbs broad range wavelength of light from ultra-violet (UV) to near-infrared (NIR). These makes this material attractive for this project.
In this project Dr. Sumaiya fabricated phase change vanadium dioxide thin-film-based light sensors using standard photolithography and lift-off process. Vanadium dioxide thin-films were deposited using pulsed dc magnetron sputtering followed by annealing. She also performed material, optical and electrical characterisations and analyse their performances. To boost-up the performance of light senor devices she introduced two novel approaches. Firstly, the reduction of device size, and secondly, with elevated temperature the photoresponse was enhanced. In both room and elevated temperature applications, the fabricated devices can detect light in a wide wavelength range, from UV to NIR. The performance parameters of these sensors are comparable to conventional and other oxide-, graphene-, and chalcogenide-based photodetectors which makes them attractive for light sensing and imaging array applications.
Project 02: Phase change material based thin-film switching devices for high speed electronics
In order to improve the speed, device density, and energy efficiency of next-generation electronics, new paradigms are urgently needed as technology begins to reach the fundamental limitations of semiconductor-based electronics. Insulator-to-metal transition (IMT) in Mott material, vanadium dioxide featuring abrupt threshold resistive switching behaviour, makes them potential for high‑speed applications such as neuromorphic circuits, radio frequency switches, quantum sensing, FETs, oscillators, and memory devices.
Lowering threshold switching voltage is essential to making the devices faster and compact. Device structures and electrode separations are two major determinants of the insulator to metal switching voltage required in vanadium dioxide.
In this project, Dr. Sumaiya explored the effect of different geometry of vanadium dioxide thin-film-based devices on IMT. She fabricated Metal-insulator-metal structures with nanogap distance between electrodes and performed material and electrical characterisations. Further, to provide insight switching mechanism in different structures of nanogap vanadium dioxide devices simulation and analytical analysis of switching performances were performed. The findings of this project are integral to designing and controlling the functional domains of phase change vanadium dioxide for energy-efficient, addressable, and scalable micro/nanoscale devices and sensor applications in future electronics.
Project 03: Solution-processed heat-blocking coatings for thermochromic applications
Thin films composed of vanadium dioxide (VO2), a well-known thermochromic material with reversible insulator-to-metal-transition near room temperature, are intriguing for intelligent and energy-efficient heat-blocking applications. However, the conventional vacuum-based deposition methods often involve a high-temperature annealing process, and oxidation of VO2 under air exposure further limits their practical applications.
In this work, Dr. Sumaiya demonstrated a room-temperature solution process to prepare VO2-based thermochromic thin films using a smart ink composed of crystalline VO2 nanoparticles. To enhance their chemical stability against oxidation and assist in the uniform deposition of the VO2 thin films, polymers were used as both capping agents and for surface modification of the VO2 nanocrystals. The concentration of VO2 nanocrystals, the type of polymers, and the molar ratio between VO2 and polymers are systematically tailored, and their effects on the thermochromic performance are also explored. This project resulted in uniform films with improved stability and switching performance on different substrates, both rigid and flexible, by dip coating, drop casting, and screen printing, offering great feasibility for further scaling up towards real-time thermochromic applications such as smart windows, smart wearables, reconfigurable electronics, smart electronic skins, and objects for defense applications.